Abstract: Free-electron laser (FEL) wavelength can continuously tuning (up to X-ray band) with high power and high efficiency. FEL has a great potential in femtosecond science, biological molecules, nano science research field and etc. In this paper, we established the self-consistent equations of self amplified spontaneous emission (SASE) FEL by using the classical particle theory and developed the steady-state Matlab-SASE-FEL numerical code. The LCLS facility parameters were optimized and the characteristic of the radiation laser light was presented. The main advantage of this code is that the data can be easily post-processed based on the convenience of Matlab tool.