Abstract: The purpose of the paper is to study the mechanism of the interaction between super low-level jet and terrain to enhance rainstorm. Using the surface observation precipitation data of Liaoning Province and ERA5 reanalysis data, this paper analyzes a sudden mountain rainstorm that occurred in the Changbai Mountains, eastern Liaoning Province on the night of 14 July 2021, focusing on the role of flow around and flow over in this rainstorm. The results show that: (1) under the favorable circulation background of the southeast of the Northeast Cold Vortex and the rear of the Subtropical High, the southward low-level jet and super low-level jet are established, which brings abundant water vapor and energy to the eastern part of Liaoning. The periodic change of precipitation is related to the intensity, location and direction of low-level jet. (2)The terrain height difference in the transition area of the mountain plain forces the airflow to generate the flow over. The vertical ascent forced by the flow over gradually weakens from bottom to top. The maximum value area is located on the mountain slope. The extremum center of regional flow over is located in the center of the rain belt, and the flow over caused by terrain is specially important to the range and intensity of the precipitation. (3)The east-west direction-dominated flow around has a certain contribution to the formation of the local vortex in the rainstorm area, and the surrounding flow plays a role in converging the warm moist current in the precipitation center, and indirectly provides an amplification effect for the air upraise. Under the combined action of flow over and flow around, the upswing branch of secondary circulation in the sloping area triggers convective development and releases unstable energy, which leads to the occurrence of local heavy rainstorms in mountainous areas.