In order to raise utilization ratio of sunlight and photoelectric conversion rate, the inner spherical focusing solar cell structure and the main performance are designed and studied. A Fresnel condenser is used to focus the sun's light onto the inner surface of a ball cavity which is prepared with polycrystalline silicon photovoltaic cells, implementing concentrating photovoltaic effect on the sphere. By using Inner cavity photon gas model, the light intensity in the inner sphere is analyzed and calculated, the concept of optimum light intensity on the silicon photocell is put forward, and the best condenser multiples for a spherical semiconductor polysilicon batteries of 18 and 9 with the layer thicknesses of 10 μm and 5 μm are calculated. Finite element analysis method is applied to discuss the inside sphere temperature of the solar system. Under the condition of the AM 1.5, 8 times concentration, photovoltaic cells′ maximum temperature is 353.15 K, in the normal scope of work. Active air cooling or water cooling method can greatly increase the convective heat transfer coefficient and decrease the temperature of the photovoltaic cells, and stabilize the work efficiency. By analyzing the constraints of the efficiency of the silicon photocell, the optimize structure of the inner spherical photovoltaic cells is designed; the fill factor can achieve 0.85, and the efficiency of the solar cells inside the spherical condenser can be more than 33% when the sunlight radiation power is 800 mW/cm2.