Experimentally exploring the difference of ultrasonic grating diffraction in non-electrolyte and electrolyte solution.The results showed that light intensity of the electrolyte solution is lower than the light intensity of the electrolyte solution,and the higher the electrolyte electrolyte concentration in the solution is, the weaker the light intensity is. By solving maxwell's equations, in the secondary approximation, the first and second level diffraction light amplitude in electrolyte solution are obtained.It is proved theoretically that because there are a lot of charged ions in the electrolyte solution, so that the diffraction intensity has obvious drop. Theoretical results are consistent with experimental phenomena.