An automatic measurement system for low frequency noises is established to sort solar cells according to their reliability. First, according to the sources of the 1/f noise of a solar cell, this paper identifies the feasibility of 1/f noise under big current density to be the reliability indication of the solar cell. Then, according to the noise spectral character measured by the automatic measurement system, it points out that comparing the 1/f noise spectrum of different solar cells in f at 1 Hz is an effective method to distinguish the reliability of different solar cells.　Finally, the method to determine the threshold of screening solar cells is given based on the standard of semiconductor device quality classification. Experimental results indicate that this kind of method can nondestructively sort the solar cells into three groups according to their reliability, and spends only 5 min for measuring single solar cell. The proposed method can detect every single solar cell correctly and has advantages over traditional methods in costs, time and hard to be hurt. This method can satisfy the application requirements of screening solar cells for high reliability.