The electricity market develop into the spot market stage, requiring higher inter-regional available transmission capacity on-line assessment require. The use of benders algorithm to solve the N-1 available transmission capacity problem, significantly reducing computing dimensions, but also proning to over-correction, oscillation and other issues. Only considering the N-1 reliability of the power grid, ignoring the lower-level power grid reconfiguration, the calculation result is too conservative, reducing the transaction volume in the cross-section. This paper presents a new method of ATC calculation based on benders algorithm. The ATC of 220kV area is analyzed taking into account of the excavation of potential power supply capacity of 110kV high voltage distribution network reconfiguration. The network reconstruction of N-1 security fault is carried out, and the ATC is improved without increasing the complexity of the problem. The problem is solved by benders decomposition method, which saves the calculation time and is suitable for on-line analysis.