This monochromator is specially designed for the F/3 holographic concave grating. Having taken into first consideration the simplicity of mechanical structure, a new kind of optical path has been designed to increase the focussing precision as much as possible. Based on Seya-Namioka Mounting and Johnson Mounting, the new design is characterized by choosing a more suitable position of the rotation axis and selecting two wavelengths for spectrum correction. The method employed is similar to that of the three point ganged tuning. The new mounting is named JS-Ⅱ Concave Grating Monochromator. So far, the results obtained have proved that the new mounting is an improvement over the Seya-Namioka and Johnson mountings. The monochromator functions within the range of 2500?→ 10000?, the loss of resolution due to defocussing being less than 1? within the range of 3500? → 6500?.