Abstract: Time-resolved transmission grating spectrometer is superior diagnostic device in laser plasma experiments. By means of it the soft X-ray spectra with excellent resolution in spectrum and time can be measured. In this paper, the principle, the construction and the performance of the spectrometer which is developed in our Lab are described at first time in China. Also, the soft X-ray emission resolved in spectrum and time from gold planar target plasmas and primary discussion are given briefly.