A newly developed high efficiency high resolution,large size transmission grating spectrograph for higher collection efficiency and higher spectral resolution used in laser produced plasma diagnosis is reported.The spectrograph comprises of a toroidal mirror as the collecting optics,a standing-free high-density transmission grating and a soft X-ray CCD camera.The partial coherent light diffraction theory is applied to determine the X-ray intensity distribution on the soft X-ray CCD camera.Analysis shows that the spectral resolution is better than 0.05 nm over the spectral range of 1.4～12 nm,which is successfully demonstrated in the relevant experiments.Owing to its high efficiency,it is especially suitable for the experiments of ultrashort femtosecond pulse laser produced plasmas.