New energies, such as wind and electricity, have been widely applied. However, for the configuration of current transformer of the output transmission line in wind farms, people still do the lectotype calculation in conventional ways. When the output transmission line breaks down, the power supply of wind farms will be weak, and a large number of aperiodic components in the faulty current will be easy to make the current transformer become saturated, which will result in the malfunction of the differential protection. In the aim of improving the reliability of differential protection, we will use PSCAD and Matlab to conduct a simulation analysis on the different saturation situation of the output transmission lines, finding out the solutions to the improvements of the reliability of differential protection. The results of simulation show that the improved recursive two-point product method can effectively prevent external mal-operations caused by the current transformer saturation. Besides, the calculation and operation time of this method can be faster, which will enhance the reliability and improve the speed of the differential protection of the output transmission line. This work is supported by Natural Science Foundation of Shandong Province (No. ZR2016EEM13) and China Electric Power Research Institute Innovation Fund Project (No. XT83-17-002).