[Objective] The creep time of rock mass generally lasts for several years, while the time for rock block to reach creep stability only takes a few hours. There is a significant difference in the creep timeliness between rock mass and rock block. On-site rock mass creep tests generally last not less than 10 days, and in some cases can reach 1 to 2 months, which can better reflect the creep timeliness of the rock mass. Therefore, on-site rock mass creep tests more accurately represent the creep timeliness of rock mass. This study aims to simulate the creep test process of on-site circular rigid plate rock mass creep test through the generalized five-parameter Kelvin creep model and to obtain the deformation expression of the on-site rigid plate creep test:$w(t)=\frac{\pi p R}{8}\left\{\frac{1}{G_{\mathrm{H}}}+\frac{1-\mathrm{e}^{\left(-G_{1} t / \eta_{1}\right)}}{G_{1}}+\frac{1-\mathrm{e}^{\left(-G_{2} t / \eta_{2}\right)}}{G_{2}}+\frac{3}{B}+\frac{3 G_{\mathrm{H}}^{2}}{B b_{2}\left(a_{1}-a_{2}\right)}\right.$$\left.\left[\frac{G_{1}+G_{2}}{a_{1} a_{2}}\left(a_{1}-a_{2}+a_{2} \mathrm{e}^{\left(-a_{1} t\right)}-a_{1} \mathrm{e}^{\left(-a_{2} t\right)}\right)-\left(\eta_{1}+\eta_{2}\right)\left(\mathrm{e}^{\left(-a_{1} t\right)}-\mathrm{e}^{\left(-a_{2} t\right)}\right)\right]\right\}$. [Methods] The generalized five-parameter Kelvin creep model consists of one spring element in series with two Kelvin elements. According to the deformation expression of the generalized five-parameter Kelvin creep model, when G₁ or G₂ equals 0, the generalized five-parameter Kelvin creep model degenerates into the Burgers model; when G₁ or G₂ approaches infinity, the generalized five-parameter Kelvin creep model degenerates into the generalized three-parameter Kelvin creep model. The generalized five-parameter Kelvin creep model is a stable model, with a long-term shear modulus of G_∞=1/(1/G_H+1/G₁+1/G₂).Therefore, the generalized five-parameter Kelvin creep model has higher fitting accuracy and wider applicability compared to the generalized three-parameter Kelvin creep model. For the generalized Kelvin five-parameter creep model, since the four variables of G_∞,G_H,G₁,G₂ and E_∞,E_H,E₁,E₂ don’t correspond one-to-one, it means that in three-dimensional rock engineering problems, the viscosity coefficient derived from the shear modulus isn’t the same as the one derived from the elastic modulus. [Results] On-site rigid plate creep tests were conducted on calcareous slate, and parameter fitting was carried out using both the generalized five-parameter Kelvin creep model and the generalized three-parameter Kelvin creep model. Key indicators during the fitting of the creep expression, such as Reduced Chi-Sqr, Adj. R², and RMSE, show that the generalized five-parameter Kelvin creep model outperforms the generalized three-parameter Kelvin creep model. Under different stress conditions, the shear modulus G₁ of the generalized five-parameter Kelvin creep model increases with increasing stress, while G₂ first decreases and then increases with increasing stress. The parameter G₁ of the generalized three-parameter Kelvin creep model also slightly increases with increasing stress, but the change is minor. The parameters of the generalized five-parameter Kelvin creep model indirectly reflect the variations during the rock mass fracture compaction stage and fracture closure stage. The long-term shear modulus of the generalized five-parameter Kelvin creep model is lower than that of the generalized three-parameter creep model. Under low stress, the long-term deformation of the generalized five-parameter Kelvin creep model increases by about 50.8% from that of the generalized three-parameter creep model; under high stress, it only increases by about 2.71%. Therefore, the generalized five-parameter Kelvin creep model is capable of expressing greater deformation, which has benefit for engineering safety. [Conclusions] The generalized five-parameter Kelvin creep model has higher fitting accuracy and can be compatible with both the generalized three-parameter Kelvin creep model and the Burgers creep model. According to the generalized five-parameter Kelvin creep model, the long-term shear modulus is lower, and long-term deformation is greater, providing a conservative evaluation of long-term rock mass deformation, which can reduce potential safety risks. In summary, the generalized five-parameter Kelvin creep model has good fitting accuracy and can provide rich information, allowing it better at reflecting the creep characteristics of rock mass.