The rectifier is an important component of the doubly salient electromagnetic generator (DSEG), which frequently bears high voltage and large current and is prone to failure. However, due to the asymmetry and non-sinusoidal nature of the DSEG phase currents, the traditional open-circuit fault diagnosis algorithms are highly susceptible to misdetection in the transient of the variable operating conditions. To diagnose the open-circuit fault in the DSEG rectifier unit, based on phase current size positional relation, a strong robustness diagnosis strategy is proposed. By theory derivation and experimental verification, it can be concluded that the proposed strong robustness open-circuit fault diagnosis strategy does not misdiagnose in the transient states of variable load, variable excitation and variable speed. And it can detect all types of single-tube and dual-tube open-circuit faults within one fundamental wave period, and has small computation and space occupation.