From the analysis on the characteristics of time effect factors in current concrete dam deformation monitoring models, this paper presented the method which applies a pre-modeling approach to optimize the preset factors of time effect, and then got some characteristics of time effect deformation by taking contrastive analysis on the simulated results obtained from actual model of horizontal displacement of some concrete dam. The investigation showed that: improperly preset factor may lead to the time effect deformation, which deviates from its basic physical meaning ； when the regression constants ' absolute value of deformation simulated results is very great, there would be a time effect deformation deformity; by classifying the time effect deformation in terms of their characteristics, the qualitative evaluation criteria of dam ' s structural state could be established, and the qualitatively monitoring index of dam safety monitoring could be set also