Frequency modulation (FM) effect on the microwave assisted switching (MAS) of magnetization has been studied by calculating the Landau-Lifshitz-Gilbert equation. Application of FM microwave can significantly reduce the switching field compared with constant frequency wave, mainly due to more effective microwave energy absorption by the spin system. The FM effect on the MAS is remarkable especially for smaller Gilbert damping of α≤0.02. For sufficient switching probability, the FM-MAS requires somewhat longer time of a few nanoseconds for the dc magnetic field parallel to the easy axis. The tilt dc field can effectively reduce the switching time.