When light emitting diodes and an infrared emitting diode are connected in parallel circuits and puton the platform,we can find the color spots of the LEDs and a white spot of the IRED on the computer screen. As a transmission grating is placed in front of the lens of the digital microscope ,a series of diffraction patternsare shown on the screen,We can measure the wavelengths of the LEDs and the lRED directly from the screen.Using this device to measure the wavelength of IRED infrared and lED visible light , the result is in goodagreement with the reference value , and the error is within 0.7%.The device has the advantages of simplicity,high accuracy and low cost. ln addition to being used as demonstration teaching,it can also allow students tooperate experiments in groups.