The invention provides a method for precisely measuring a grating slice spacing based on the refractive principle, relating to the grating spacing measurement. According to the method, a magnifying glass is used to detect the spacing size of an actual grating sheet; computer plate making design software is used to design black and white lines with an equal distance, and a printing dedicated slice machine to print the black and white lines with an equal distance to a film; the printed film is covered by the grating slice, black and white lines with different distances shows black and white patterns with different sizes on the grating sheet, each black and white line shows a black and white pattern with an equal distance in the grating slice, and a measurement calculation formula is created after the related data measurement of the black and white lines; With the calculated data as a basis, the spacing of the grating slice is obtained, a printing dedicated film is printed again through computer software to verify whether data is corrected, and if obtained patterns are all black or white, the distance of the black and white lines and the spacing of an actually used grating slice are the same.