Fiber bragg grating (FBG) sensor monitor has been widely applied in civil engineering, yet it is less used in hydraulic geomechanical model test. Based on the geomechanical model of Lizhou arch dam on Muli River, we arranged FBG sensors on the crest and upstream surface of the dam to monitor the dam strain in the process of overload. Through the strains and variation curves obtained by FBG, we analyzed the cracking propagation on the arch dam surface. Results showed that when Kp=1.0, the dam was in normal condition; when Kp=1.2-2.2, initial cracks appeared at the dam heel; when Kp=2.2-3.0, inflexion points of the strain curve occurred, which revealed large displacement of the rock mass in the left bank abutment; when Kp=3.6-4.3, the strain curve fluctuated sharply on the whole, with cracks on the left arch; subsequently, the strain curve fluctuated  successively, indicating that the cracks on the dam developed steadily until failure happened. Comparison with the results from strain gauge verified the feasibility of applying FBG to geomechanical model test.