Abstract: Based on regional model simulations of a typical case of an eastward-moving Southwest vortex with the eastern retreat of a subtropical high (case 20150721), this paper discusses the effect of the strength of the subtropical high on the eastward Southwest vortex based on a numerical sensitivity test of a subtropical high enhancement. The main results are as follows: (1) An enhanced subtropical high can be stably maintained for a long time and can have a lasting impact on the development and evolution of the entire Southwest vortex meso-scale system. The area and intensity of precipitation directly depends on the path and intensity of the Southwest vortex. (2) The circulation field first changes when the strength of the subtropical high increases, the invading north wind becomes weaker, and the southwest guided airflow becomes stronger, which eventually results in a faster and weaker Southwest vortex. (3) The change in the circulation field directly affects the transport, convergence, and divergence of the water vapor, and further affects the whole evolutionary process of the Southwest vortex. (4) After the increase in the subtropical high, the faster Southwest vortex results in the deviation between the center of the Southeast vortex and the thermal center in the lower layer, which causes a mismatch between the dynamic and thermal centers and a weakening of the strength of the Southwest vortex.