Silicon micro-cantilever resonators are typical elements in micro-electro-mechanical systems. Basing on the photothermally excited micro-cantilever resonators, many optical microsystems can be realized, such as micro-swichtes,mciro-modulators and microsensors etc. In this paper, mechanism and experiment study is given on photo-thermally excited bi-layered silicon micro-cantilever resonators, and relative results can be served as the basis of further applications. When coating is put on the surface of micro-cantilever to increase the optically exciting efficiency, the whole resonator becomes bi-layered structure, and the mechanism of this bi-layered resonator is very different from those of single material resonators. In this paper, photo-thermally excited mechanism of bi-layered silicon micro-cantilever was presented and a corresponding photo-thermal theoretical model was set up based on the photo-thermal effect. The first three resonant modes of the silicon micro-cantilever were detected successfully by using piezoelectric resistors fabricated as a Wheat-stone sensing bridge on the micro-cantilever. A novel method was presented to excite and detect the microresonator at the same time by using only one optical source , and this novel method was demonstrated by detecting the first resonant mode of the micro-cantilever.