The online security and stability analysis data is composed of local state estimation data and data of other dispatching agencies issued by the superior. The power deviation of the regional tie line is caused by the synchronization of the time between the two. In this paper, a method of regional tie-line power flow adjustment is proposed for data splicing of internal and external networks. On the basis of aggregation of interconnection lines into contact channels and several nodes with greater sensitivity to the aggregate nodes, the adjustment quantity is obtained by solving the linear equations of aggregate node adjustment quantity and connection channel power flow deviation quantity. When the system is ill-conditioned, the problem of no solution of linear system is avoided by solving minimum norm least squares solution. This method can meet the requirements of speed and accuracy of online safety and stability analysis. The validity of the method is verified by the case of actual power system.