Abstract: Based on the principle of grating diffraction, by using television measuring system to measure the offset between the imaging of incident laser and the optical axis to confirm the angle of incidence and the angle of diffraction of the grating, a method of measuring incident laser wavelength in far field with grating is brought up.The measurement principle and the optical system of this method are introduced.The expressions of calculating laser wavel ength are educed in detail.The expressions of calculating the precision of wavel ength measurement are presented,after analyzing the structure of measurement system.The feasibility of this method is testified by the simulation experiment of far field measurement.