In this paper, a magnetron-driven system with simple preheat method and power modulation is presented. Since the resonance microwave transmission of the magnetron requires a stable DC high-voltage and an AC preheating voltage, this paper is devoted to simplifying the system architecture while a sufficient resonant gain to drive the magnetron is ensured. In this design, a simple preheating method using the filament coil of the magnetron is also adopted to achieve the preheating requirement of magnetron, which is followed by the utilization of a frequency modulation approach to stabilize the output voltage. To confirm the feasibility of this proposed system, the hardware realization of a 1.3 kW prototype is completed. Experimental results have demonstrated the effectiveness of this magnetron-driven system for microwave industry applications.