Abstract: High power narrowed linewidth pump source is needed with diode pumped alkali laser developed. But the linewidth of the commercial diode laser is far exceed the absorption linewidth of the alkali atom. So the Littrow external cavity is used to narrowed the spectrum of high power diode laser array. The linewidth of high power diode laser array is directly affected by the parameters of elements in Littrow external cavity. In this paper, the model of external cavity diode laser was set up by using ray tracing method. By replacing cylindrical lens with sphere lens, the influence of micro-cylindrical lens array, beam shaping optics and grating were analysed. The resutls show that, to obtain narrower output laser linewidth, the focal length of micro-cylindrical lens array should be smaller, the grating grooves is denser, and the focal of spherical lens is larger. And the theoretical conclusions is demonstrated by experimental results.