Static var compensator (STATCOM) is a widely used power electronic device for dynamic reactive power compensation, and its current detecting and control method generally adopts d-q decoupling method based on the synchronous rotating coordinate transformation. However, in the traditional method, the load reactive current component is directly used as the command of STATCOM output current, so it is required that the installation position of STATCOM must be consistent with load current detecting point. But in practice, STATCOM installation point and load current detecting point may be located at two different sides of the transformer. For this situation, this paper proposed an improved reactive current detecting and control method based on the principle of power balance, achieving the current detecting and control strategies when the two points are located at different sides of transformer. Finally, the simulation of system with STATCOM accessed from the third winding of transformer verifies the correctness and feasibility of the proposed method.