In the late spring and early summer of 2021, many regions in China experienced abnormal rainstorms and severe convections, causing heavy casualties and property losses, especially in southern China (25°~32.5°N,112.5°~122.5°E) from May 10 to 16. In order to investigate the potential causes of the frequent severe convection outbreaks in southern China from a perspective of largescale environment, the present study analyzed the features of the atmospheric circulation anomalies during 10-16 May,2021, as well as the associated dynamical, thermal and moisture conditions. The results show that the outbreaks of severe convections are closely related to large-scale circulation anomalies. At 500hPa, the geopotential height anomalies exhibit a northwest-southeast oriented wave train pattern with a “+-+” distribution. Along this wave train, the Ural Mountains and the coastal regions of East Asia are dominated by positive height anomalies, while the Lake Baikal are occupied by negative height anomalies. The positive anomaly along the East Asian coast corresponds to an intensified and northward shifted western Pacific subtropical high (shorted as WPSH). The anomalous southwest warm air flow to the north of the WPSH is beneficial to the development of ascent as well as the establishment of unstable stratification in southern China. On the other hand, the anomalous warm advection makes the pressure decrease in the lower layer in southern China, so the systems such as surface convergence line, front and low-layer shear line occur frequently, which would trigger severe convections. In addition, the strong vertical wind shear formed between high and low-level jets is also one of the favorable dynamic conditions for the development of severe convective system. Further analysis indicates, there is a southeastward propagating anomalous wave activity flux that originates from the high latitudes of Eurasia, suggesting the wave train-like circulation pattern is closely associated with the dispersion of the Rossby wave energy. Therefore, the anomalies of atmospheric dynamical process in mid-high latitude play an important role in the frequent severe convections in southern China.