The minority carrier lifetime is the key parameter of the semiconductor material. Through the study of minority carrier lifetime, the recombination mechanism of the carriers can be understood, thus the material can be sampled effectively. The yield and the performance of infrared detector will be raised. The minority carrier lifetime measuring system is designed by the method of photoconductive decay (PCD). The double refracting-reflecting optical system is adopted, so the sideview and bottom view of metal Dewars can be used for testing. There are two testing methods: Auto-test and Semi-Auto test. The range of the measuring system is from 1×10^-7～6×10^-6sec.. The diameter of measured sample must be less than 20mm.