Developing of a time-resolved three-channel soft X-ray spectrometer is reported，and the operating principle and the parameters of spectrometer designed in three energy bands of 210eV，420eV and 900eV are presented specially. On the ShenGuang-Ⅱ high power laser facility，the spectrometer was applied in experiments with good results. This work is the first attempt in China to construct a spectrometer which couples planar mirrors and filters to X-ray streaked camera，and which is capable of measuring X-ray signal with spatial- and temporal-resolution in three sub-Kev energy channels simultaneously. Experimental results show that by combining X-ray reflector and filter，the spectrometer has achieved enery resolution of 5 and temporal resolution ability of 10 ps.