Abstract: With the increasing scale of the inter-provincial transmission, the number of the inter-provincial and inter-regional transmission channels gradually increases and couples closely, and the traditional Available Transmission Capacity (ATC) cannot reflect the influence of the intra-provincial security constraints on the inter-regional transmission power range and the coupling relationship between the regional contact lines. Based on the feasible domain projection theory, this paper proposes the concept of inter-provincial multichannel contact line available transmission power security domain, and the inter-provincial multichannel contact line security domain portrayal method considering the provincial generation situation, the load characteristics and the network constraints in order to realize an efficient and fine portrayal of the feasible domain of the multi-link, large-scale inter-provincial power system model. The proposed safety domain-based inter-provincial market optimization clearing model meets the inter-provincial market clearing target demands and considers the intra-provincial constraints, achieving the efficient cooperative operation without the iteration across provinces. Based on the interconnection system of the IEEE 39 and the IEEE 118 nodes, we simulate the inter-regional power trading, and the calculation results verify the effectiveness of the proposed model.