To enrich the swirl flow theory of moving boundary, the hydraulic characteristics of the swirl flow produced in hydrocyclones with different guide vane heights were analyzed by combining theoretical analysis and model test. The results show that the pressure of the test section was positively correlated with the guide vane height of the hydrocyclone. The influence of hydrocyclone on the flow characteristics of the rear section was greater than that of the front section. With the increase of the guide vane height of the hydrocyclone, the downstream axial velocity of the test section increased first and then decreased, the radial velocity gradually decreased, and the circumferential velocity first decreased and then increased. The existence of the guide vane of the hydrocyclone increased the axial velocity near the pipe wall, the radial velocity near the pipe wall was negative and the radial velocity at the center of the pipe was positive. When the guide vane height of the hydrocyclone was 15 mm, the axial velocity of the test section was the maximum, and the changes of circumferential velocity and radial velocity were the minimum, and their distributions were relatively uniform. Therefore, the hydrocyclone with guide vane height of 15 mm had the best hydraulic performance.