Abstract:In middle ten days and last ten days of February in 2006, there were tow preci pitation processes in Changjiang delta, i.e. snow and rain respectively, but the forecast of precipitation type was wrong. A comparison of these two processed s hows that in the snow process, there was west wind in the front of trough and th e circulation was flat, whereas in the rain process, there was southwest wind in the front of trough. Snow would happen only if the cold advection, which was r esulted from the northeast return current, generated a cold center over east Chi na. However the north and northwest wind decreased the air temperature, but no precipitation would happen at the same time, so there would be no snow in this case. Before snowing the air at 850 hPa was dry and before raining the air at low middle levels was wet. Th e temperatures at 700～800 hPa and in the inversion layer were important to the precipitation type. At the end of snow process the air in high level become dry first, whereas at the end of rain process the air in middle level become dry fi st. In snow process the snow and ice crystals were centralized in the high le vel, and the center of snow content was at 600～700 hPa. In rain process, the l ower boundary of snow content lifted up and its center was in a level above 600 hPa. The center of snow content weakened very fast when it moved down northward s.