Ag₂ZnSnSe₄ is an n-type semiconductor with a suitable bandgap of 1.4 eV. In the present study, a graphene/Ag₂ZnSnSe₄ induced p-n junction thin film solar cell is proposed and the physical mechanism and performance influencing factors of the solar cell are simulated and analyzed by using the wxAMPS software. The simulation results show that when a high work function graphene contacts an n-type Ag₂ZnSnSe₄ semiconductor, the energy band of the Ag₂ZnSnSe₄ absorber layer bends upward, meanwhile a p-type Ag₂ZnSnSe₄ inversion layer is induced on the surface of n-type Ag₂ZnSnSe₄, therefore the p-type Ag₂ZnSnSe₄ and n-type Ag₂ZnSnSe₄ form an induced p-n homojunction. It is found that the work function of graphene and back contact significantly influence the photogenerated carrier separation, transportation and collection. The graphene work function should be 5.5 eV and the work function of back contact should not be greater than 4.4 eV, which is beneficial to the improving of the device performance. The doping concentration of Ag₂ZnSnSe₄ absorber mainly affects the short-circuit current of the device, however, the defect density of Ag₂ZnSnSe₄ absorber affects the whole device performance. When the work function of graphene and back contact are 5.5 eV and 3.8 eV, the doping concentration and defect density of Ag₂ZnSnSe₄ absorber are 10¹⁶ cm^–3 and 10¹⁴ cm^–33, respectively, the conversion efficiency of the graphene/Ag₂ZnSnSe₄ induced p-n junction thin film solar cell can reach 23.42%. These simulation results provide the idea and physical explanation for designing a novel type of solar cell with high efficiency and low cost.