A robust SE model is introduced for AC/DC hybrid system. First, to simplify its formulation, the SE model is transformed into an equivalent form by introducing equality constraints and new variables. In this model, the hybrid system is formulated as a whole. Then, an interior point method is used to solve this problem. And an approximating technique is proposed to guarantee the Hessian matrix positive definite, which can significantly improve the efficiency of the solution. Five numerical tests with IEEE 9 node system, IEEE 14 node system, IEEE 30 node system, IEEE 118 node system, and IEEE 145 node system show that the proposed algorithm is efficient, robust and reliable. It has the potential to be applied in real application.