Commutation failures may lead to serious consequences such as DC blocks. A simulation method of joint using the electromagnetic transient program and the electromechanical transient program is presented to analyze commutation failures. This method is realized in two steps. Firstly, the commutation failure critical voltage under a certain operating condition is determined with PSCAD/EMTDC. Secondly, this critical voltage is used in PSS/E, an electromechanical transient program, to analyze commutation failures of AC-DC systems. Using the proposed method, the effect of AC faults on commutation failures of a practical DC link in China is analyzed. Voltage contours is also utilized to improve the visualization of commutation failures. The combined simulation method, which gives consideration to both the simulation accuracy and the simulation efficiency, is beneficial to better analyze commutation failures of large-scale power systems.