Based on the second law of thermodynamics,a theoretical model is established for efficiency analysis and optimization of a solar thermophotovoltaic (STPV) system. The entropy generation in the photo-electricity conversion process is numerically calculated and analyzed for the component modules involved in the whole system assembly. The effects of the emitter temperature,concentration ratio,energy bandgap,cell temperature and the transmissivity of the filter on the entropy and the efficiency are investigated. Meanwhile,the conversion efficiencies of the modules are discussed. The following results are obtained:at first the entropy generation of the system reduces but then increases with the rise of the emitter temperature. When the concentration ratio improves,the entropy generation of the system falls. The increase of the bandgap value and chemical potential of the cell also causes the reduction of the entropy generation. Along with the increase of the cell temperature,the entropy generation increases and the conversion efficiency of the STPV system decreases. Based on the second law of thermodynamics, a theoretical model is established for efficiency analysis and optimization of a solar thermophotovoltaic (STPV) system. The entropy generation in the photo-electricity conversion process is numerically calculated and analyzed for the component modules involved in the whole system assembly. The effects of the emitter temperature, concentration ratio, energy bandgap, cell temperature and the transmissivity of the filter on the entropy and the efficiency are investigated. Meanwhile, the conversion efficiencies of the modules are discussed. The following results are obtained: at first the entropy generation of the system may but then increases with the rise of the emitter temperature. When the concentration ratio improves, the entropy generation of the system falls. The increase of the band gap value and chemical potential of the cell also causes the reduction of the entropy generation. Along with the increase of the cell temperature, the entropy gene ratio increases and the conversion efficiency of the STPV system decreases.