In this paper, we performed the numerical and experimental study of unsteady cavitation surge around a semi-circular leading-edge flat plate using a passive flow control method. We mounted a miniature spanwise wedge-type vortex generator on the suction side of the model close to its leading edge. To mitigate the destructive impact of this type of cavitation on the hydrofoil performance, we analyzed the effects of the passive control on the dynamics of cavitation surge. First, we investigated experimentally the unsteady cavitating flow around the semi-circular leading-edge flat plate without passive control using high-speed visualization, acoustic measurements and particle image velocimetry method. Next, we simulated numerically the dynamics of unsteady flow under the cavitation surge conditions with an open source code and validated the numerical results using the experimental data. We used a proper interaction between turbulence and cavitation model to capture a highly unsteady behavior of cavitation surge. Finally, we considered the effects of the passive control device on the mechanism of the cavitation surge instability. Our results revealed that using the passive control method, it is possible to stabilize the attached cavity on the suction side of the flat plate, to hinder the development of the spanwise instability of the attached cavity and to mitigate large-scale cavity structures. Furthermore, high-pressure pulsations in the wake region induced by unsteady cavitation surge were considerably reduced.