Abstract: Coupled with the 3-beam laser Doppler anemometry(LDA),the amendment of the measuring parameters in different media was discussed in theory. And the amendatory formulas were achieved. With the formulas,the parameters both in air and in water were obtained and compared. The result proved the amendment of the parameters was correct and necessary. The mean velocities were gained individually in the reduction fluid by LDA and flowmeter. By comparing the two results,it proved the LDA was trustiness.