Abstract: This paper is to analyse the structure of the mesoscale rotational rain belt of Typhoon 9012(YANCY)and its relationship with the heavy rainfall in north east of Fujian. We can see that the mesoscale rotational rain belt orginated from the asymmetrical wall of Typhoon eye and transmited in pulse along diameter. In front of the rain belt ,there was a medium depression, with which the disturbance and gravitational wave are quite consistent. Affected by the sea land and terrain,the rain belt tends to streng then. With some special terrain, the precipitation can be 1-3times as much.