Base on Shum an-Shapiro mesoscale filter, high-pass filter under the background of large-scale circulation and analysis of satellite image and radar echo, the heavy rain in the central Yunnan on June 17, 2003 is analyzed. It shows that the rain can be attributed to the southeast movement and the development of a tropical mesoscale cyclone. The invasion of surface cold air to the mesoscale depression leads to the development of convective activities and the tropical mesoscale cyclone. The tansportation of water vapor from the Bay of Bengal, the South China Sea and west Pacific Ocean in large-scale circulation provides the energy to the development and maintenance of the strong convection. The center of the surface mesoscale depression and the north of the shear line are indicative to the rainfall area.