Referring to the shortage and limitation of ruled grating which has ghost line and stray light because of period error and ruling irregularity,a method for making a Wavelength Division Multiplexer(WDM) is proposed based on Micro Electro-mechanical System(MEMS) blazed grating.The basic composition of WDM based on MEMS blazed grating is introduced according to the method.The craft for realizing MEMS blazed grating and the means for improving diffraction efficiency are also introduced.MEMS blazed grating is numerically simulated and analyzed in Laboratory Virtual Instrument Engineering Workbench(LabVIEW).And the diffraction intensity distribution of blazed grating is presented.At the same time,the rays in WDM are traced in ZEMAX.The results prove that MEMS blazed grating can be applied well in WDM.