A model and algorithm of interconnection optimal power flow（OPF），which considers the trade power constraints of transmission interface，is provided for interconnected power grid. The objective of the OPF model is to minimize the active power loss to guarantee the optimal operation of interconnected power grid. The active power constraints of transmission interfaces between each regional power grid are considered to satisfy the trade power constraints of the interfaces. The operation feasibility constraints of each variable are included in the proposed model. Considering the interconnected power grid is formed by multi-area power grids，the border bus is copied and the interconnected power grid is divided. A decomposition-coordination OPF model is established based on the proposed interconnection OPF model. The decomposition-coordination interior point method is used to solve the decomposition-coordination OPF model. The decomposition-coordination OPF model and decomposition-coordination interior point method can improve the computational efficiency. The simulations for the four test systems demonstrate the correctness and effectiveness of the proposed optimal power flow model and algorithm.