Based on the dense observation data, satellite images and reanalysis data, the reasons of Meiyu heavy rainfall in Zhejiang on 13 June 2017 are analyzed. The results show that low-level easterly and southwest winds could bring significant water vapor and energy, and Typhoon Merbok had an important role on the southwest air transport. The non-hydrostatic WRF V3.6.1 model was used to simulate heavy rainfall at high resolution with two nests. The sensitivity experiments show that Typhoon Merbok can enhanced south wind transport to Zhejiang, making the northeastern and southeastern flows meet in Zhejiang. The gradient of the north and south winds increased obviously, which made convergence streng-thened obviously. Meantime, “Merbok” enhanced the water vapor transport. A convergence in the left side of the mid-low-level southwest wind was accompanied by a divergence on the right side of the upper-level jet. This was conducive to the occurrence of vertical motion, promoting the increase of rainstorm. Sensitivity experiments show that the stronger the typhoon, the more water vapor transport in southwest flow, the stronger convergence, the more conducive to the development of vertical motion and convection, and the heavier the precipitation.