In configurations with diffraction grating in Littrow mount, putting a grating and a mirror on the plane which can be rotated, and letting the rotating axis of the plane doubling with the cross line between the grating and the mirror, we develop a compact and tunable light source. There is not any position change of output light beam when being tuned, and the rectangle facular of the output laser has been compressed to quasi-square through a prism. The size of the light source is 110 mm×80 mm×35 mm, and the output width is 0.07 nm, and tuning range is 4.6 nm. From experiment it can operate for 4 hours without any change of output light.