A novel soft X-ray spectrograph comprised of a toroidal mirror image optics, a high-density transmission grating and a soft X-ray CCD camera has been developed. The detecting range is in the wavelength region from 0.5 nm to 15 nm with a resolution of about 0.05 nm. The spectrograph has no astigmatism. A point object is imaged to a point. Owing to its high efficiency, even an X-ray spectrum of low-energy laser produced plasma can be measured. It is especially suitable for experiments of ultrashort femtosecond pulse laser produced plasmas.