First,the method of quantum efficiency calculation is analyzed in the paper.Then,the test process of MCT detector is analyzed.Based on the test results of electrical parameters and spectral response of the device,the number of electrons produced by the detector is calculated by the test method and test data.By comparing the actual electronic number with the theoretical photon number,the quantum efficiency of infrared detector for different brands is calculated,which can be up to 66 %,reaching the quantum efficiency index of the response of the same type of devices abroad.This study provides an effective method for evaluating the photoelectric conversion performance of HgCdTe detector.