Abstract: The charcateristics of microburst were described, and the Doppler velocity field structure of a wet-type microburst occurring on July 22, 1997 in Beijingar eahas been researched. Using no nhydrostatic compressible meso-γ model, the main structure and evolution processes of this wet-type micro burst lines have been simulated, and the result of the simulation is very close to the measurement of the Doppler radar. The result shows that, under the environment of high temperature, high humidity, but with small vertical wind shear, the evolution of the dow ndraft is not fully supported by the negative buoy-ancy due to temperature decrease by evaporation and melting. On the contrary, precipitation trailing force play samain role in the procedure. This paper point sout that, in different environment conditions, cloud-physics for the evolution of the microburst may be very different.