We report a novel optical microcavity based on the Fabry–Perot (F–P) microcavity, which is a roof structure with two top reflectors that are symmetrical structure and proper inclined angle. The special design of the top reflectors increases the one-period-length for the mode light ray inside the microcavity and confines light in a smaller area effectively. The resonance principle of the microcavity is analyzed, and simple analytical expression of the resonant wavelength and resonant condition of the microcavity are given. The properties are numerically studied by the finite element method. Simulation results of the microcavity with small incline angle are almost consistent with theoretical analysis. Compared with the F–P microcavity, the result show that the proposed microcavity has outstanding advantages such as high quality factor, narrow spectrum, and small effective mode volume, which has a great potential in photonic devices and optoelectronic devices.