The influence of grating height on the diffraction efficiency of SU-8 micron gratings was studied.The diffraction efficiency of gratings with heights of 6-8 μm, 12-16 μm, and 6-30 μm was simulated and analyzed using rigorous coupled wave theory. The simulation results show that when the grating height is 6 μm, the 0th order diffraction efficiency is the lowest and the 1st order diffraction efficiency is the highest; At 12 μm, the 0th order diffraction efficiency is the highest and the 1st order diffraction efficiency is the lowest. When the grating height continuously changes from 6-30 μm, the diffraction efficiency varies periodically. SU-8 thin films with different thicknesses were prepared, and 40 μm periodic gratings with different gate heights were fabricated using picosecond laser etching technology. The measurement results show that when the grating height of the 40 μm period grating is 6.83 μm, the -1st order diffraction efficiency is 28.4%, and the 0th order diffraction efficiency is about 14.7%; When the grating height is 13.45 μm , the 0th order diffraction efficiency is 31.46% and the 1st order diffraction efficiency is 12.35%. The magnitude of the 0th and 1st order diffraction efficiencies varies with the grating height period. The theoretical simulation and experimental exploration can provide important references for the preparation of SU-8 micron gratings and the improvement of first-order diffraction efficiency.