Numerical simulation is carried out for a heavy rainfall event influenced by two typhoons to study the mesoscale vortex related to the event. The results show that: (1) the rainfall event was jointly influenced by continental high, Typhoon Fitow and Typhoon Danas. Obvious mesoscale vortex activity was found in the midtolower levels during the event. (2) Vertical vorticities related to the vortex started to develop from the lower level of atmosphere. At first, vorticities concentrated below 850 hPa, and then strengthened upward. Meanwhile, the vortex was growing in size and intensity, and finally became a deep mesoβ scale vortex accompanied by closed cyclonic circulation. (3) The terms of horizontal advection, vertical advection, convergence making and tilting of local vorticity tendency had different effects in different times and levels. The convergence making term was the main contributor to the midtolower level vorticity source. The vertical advection term was the main contributor to the upperlevel vorticity by transporting lower vorticity to the higher levels. The tilting effect had some influence on the development and movement of the vortex. (4) The latent heating effect of precipitation had important influence on the development and movement of the vortex. It changed thermodynamic condition and stability of the atmosphere. Therefore, it was responsible for the maintenance and development of the convergence and convection term of the local vorticity tendency.