With the development of HVDC transmission systems

the power flow calculation dominated by AC power grid is bound to face fundamental problems of handling the HVDC transmission unit and the link mechanism. Such being the case

according to the basic equations of DC transmission units and the connectivity of various control modes

the current is taken as a state variable in the power flow calculation to make the DC transmission unit organically combine with AC power system. Based on the above

the DC/AC hybrid power flow equations are established and Newton iteration algorithm is applied to solving the model. On the premise of the link mechanism of AC/DC power system

the study aims to minimize the dimension of the Jacobian matrix and realize direct observation of the operation state of the DC transmission unit

providing a basic tool to evaluate or control the AC/DC system. The algorithm is proved effective with a 22-bus system. This work is supported by National Natural Science Foundation of China (No. 51177091).