The purpose of this work is to determine ways to increase the performance of available power transfer capacity analysis with transient stability constraints, as well as to evaluate the accuracy of the proposed methods. A number of developed methods for performance improvement of available power transfer capacity (APTC) analysis with transient stability (TS) constraints in the stability margins monitoring system (SMMS) were discussed in this article, in particular: network reduction, transient stability analysis with implicit integration method, parallel computing of contingencies, and sequential TS simulations startup. In addition, evaluations of the method's accuracy of APTC calculations with TS constraints for various power transmissions were carried out. © The Authors, published by EDP Sciences.