In this work, we validate the application of GATE (Geant4 Application for Tomographic Emission) Monte Carlo simulation software to model a GE eXplore VISTA small animal PET system. GATE was used to build our three-dimensional PET simulation model. The simulated acquired data were stored in a list-mode file and processed by the same reconstruction scheme as that used in real scanner. To validate the simulation results, several phantoms used in performance assessment experiments were modeled for simulating the system sensitivity, spatial resolution, scatter fraction and count rate response. A realistic voxelized mouse phantom was applied to present the overall quality of our model and compared with mouse images obtained from real exam.