Power converters are important components of power conversion transmission in wind power generation systems, and open circuit failures can cause unplanned downtime of wind power generation systems,so it is especially important to diagnose the open fault of the power converter. In this paper, the influence of space vector pulse width modulation (SVPWM) on the sector affected by the open circuit fault of the power switch and the change of the basic voltage space vector are analyzed. In this paper, according to the comparison of the sector numbers of SVPWM modulation before and after the failure of the power switch, a method for judging and locating the open circuit fault of the power switch is proposed. Compared with the existing diagnostic methods, the method can realize single-switch and double-switch open-circuit fault diagnosis, and only needs to collect a single variable of the sector number in SVPWM modulation, without adding additional hardware equipment, low data storage requirements, simple calculation and easy to implement. Finally, the effectiveness and feasibility of the proposed open circuit fault diagnosis method are verified by simulation and experiment.