Abstract: At 2pm 16th of March,the cold Ps(Polar Siberian) air mass was on the way to invade China Proper. The discontinuity as seen by wind direction along the cold fronts extended from Inner mnngolia to North China, The warm front treaded SW-ward at a distance of about 200km, west of Nanking. The temperature in the warn setter ranged from 15℃, to 20℃,while that to the east of the front was mostly five to ten degrees lower, As showen by the sounding balloon observation taken at Pei-Chi-Ko in the afternoon of the 16th, the frontal inversion was 3,330m, in height over Nankingt which was nearly the height of A-St, observed by the pilot balloon simultaneously, The layers, from the surface to 2.22km and from 3.05km, to 3.33km, were in conditional instability, But that from 2.22km, to 3.05km, was absolutely stable, The moist and cool Yp (Polar Pacific)air mass below the frontal inversion seems to be NPs (transformed Polar Siberian),which returned from the relatively warm ocean as a SW-ly or SE-ly current, Above this inversions the tropical air mass was is a state of absolute stability which was probably due to the modification during its N-ward journey, This may explain why no preci pitation was raceived in the regions to north of the Yangtze during the passage of the frontal systems.