Abstract: Based on the wind stress field observed along the coast of the Bohai Sea and the Yellow Sea from 1978 to 2015, the spatio-temporal modes and interannual variation on the seasonal cycle of monthly mean wind-driven current field in the Bohai Sea and the Yellow Sea were studied with methods of two dimensional nonlinear vertical average wind-driven current model, Rotated Empirical Orthogonal Function (REOF) and harmonic analysis. The results show that the seasonal cycle of monthly mean wind-driven current velocity potential and stream function field are divided into two spatio-temporal modes. The seasonal periodic component is the main component of the spatio-temporal modes. Due to seasonal variation of monthly mean wind stress field, the seasonal spatial and temporal variation of the stream function field in the Bohai Sea is greater than that of the velocity potential field, and the second mode of velocity potential and stream function field are the main component of seasonal variation. The seasonal spatial and temporal variation of the velocity potential field in the Yellow Sea is greater than that of the stream function field, and the second mode of the velocity potential field is the main component of the seasonal variation. Due to the interannual variation of monthly mean, the wind stress field strength in the Bohai Sea and the Yellow Sea decreases significantly and linearly while the interannual variation of seasonal mean wind-driven strength decreases significantly. The seasonal growth and disappearance of warm current and cold water mass in the Bohai Sea and the Yellow Sea is the interaction results of wind-driven current due to horizontal circulation and vertical convection of cold-warm water mass transportation and convergence. The convergence upwelling circulation during spring and summer in the Bohai Sea and the Yellow Sea delay the transmission of shallow warm water to the deep layer, and was an important driving force for the formation of cold water mass and thermocline in spring and summer. Therefore, the velocity potential is a very important factor in the study of the Bohai Sea and the Yellow Sea wind-driven current field. The anticyclonic and divergence downward circulations in central Bohai Sea and the eastern Yellow Sea, the cyclonic and convergence upwelling circulation in central Yellow Sea in winter are the main dynamic control factors for the seasonal transition and intensity of the Yellow Sea Warm Current. The cyclonic and convergence upwelling circulation in eastern Yellow Sea, the anticyclonic and divergence downward circulation in central Yellow Sea in summer are the main dynamic control factors for the seasonal transition and intensity of the Yellow Sea Cold Water Mass.