A kind of double-layer Si-based microcantilever was fabricated using standard integrated circuit and micro-mechanical machining technology. It was thermally-excited and the signal was detected based on piezoresistance effect of semiconductors. Taking the advantage of FPGA, the digital closed-loop system on silicon resonant microcantilever was implemented. On this basis, the resonant characteristics like amplitude of output signal, the resonant frequency shift, the frequency stability and the quality factor of this kind of microcantilever were studied through theoretical analysis and experiment. This paper focus on the dependence of amplitude of output signal on the exciting power, bias voltage as well as the dependence of resonant frequency shift of output signal on the exciting voltage, bias voltage. Analysis about the result of the experiment was given, which showed that this silicon microcantilever is suitable for resonant microsensor, and provided some advices for the optimum design of the system. It laid the foundation for the development of a new resonant structure of silicon micro-cantilever sensors.