The purpose of studying the 1/f noise spectrum of IR detector is to learn its the surface treatment situation and reduce the transition frequency of the 1/f noise spectrum. After briefly introduction of the 1/f noise, the measurement principle of the 1/f noise and the measuring system configuration are explained in the paper. Finally, the curves of the 1/f noise spectrum for typical HgCdTe PC/PV detectors are given and the analysis of these curves are made.