The performance variations of CdTe solar cells at low light intensity were investigated. The solar irradiance dependent models of main parameters including the short circuit current, the open circuit voltage, the fill factor and the efficiency were confirmed, then the variations of the main parameters with the intensity of 0.02~1kW/m2 were discussed. It is shown that with the decrease of the solar intensity, the short circuit current of the CdTe cell decreases linearly, the open circuit voltage shows an exponential decline, the fill factor increases firstly unitl reaching the maximum value beside the point of 0.3kW/m2 and then drops rapidly. The conversion efficiency deteriorates gradually. It provides theoretical guideline for outdoor low intensity and indoor applications of CdTe thin film solar cells.