In allusion to the situation that the traditional algorithms do not apply to power flow calculation of integrated transmission and distribution network, this paper constructs a cooperative power flow calculation algorithm. Based on the electrical connection relationship and structural characteristics of these two networks, the algorithm makes region division, builds boundary mapping area, processes mismatching power and discusses convergence judgements. According to the structure characteristics in different regions of distribution, appropriate algorithm is used for each division. A treatment method is given when the load power is manually set. The transmission and distribution network of Guangzhou is taken as a test case and the result shows the accuracy and multi-suitability of this algorithm.