Conventional operation strategy of silica gel-water adsorption chiller in solar cooling application uses fixed cycle time, but it deviates from real optimal cycle time because of varied solar hot water temperature. Mathematical model and simulation of a solar silica gel-water adsorption chiller was done and performance comparison in two operating strategies (fixed and varied cycle time) was made according to experiment data of a real solar system. An estimating equation for the optimal cycle time was developed by the simulation results, considering both COP and SCP by a weighting factor. Correlation of optimal cycle time and hot water temperature was fitted in a linear equation. Optimal half cycle time decreased with increasing hot water temperature and weighting factor. COPs of varied cycle time were much larger than those of fixed cycle time whereas SCPs of varied cycle time and fixed cycle time were nearly the same. So operation strategy of silica gel-water adsorption chiller with varied cycle time can significantly improve the whole utilization efficiency of solar cooling system without any decrease in cooling capacity.