The invention provides an optical resonant cavity formed by non-parallel reflecting mirrors and a method for generating optical resonance. The optical resonant cavity comprises a top reflecting mirror and a bottom reflecting mirror, and is characterized in that a cavity is formed between the top reflecting mirror and the bottom reflecting mirror, and the cavity is filled with a medium; the top reflecting mirror comprises two oppositely arranged plane reflecting mirrors, and the two plane reflecting mirrors have the same inclination angle relative to the bottom reflecting mirror; and the bottom reflecting mirror is a plane reflecting mirror. According to the invention, the resonant cavity is provided with the inclined top reflecting mirror, so that an incident beam perpendicular to the bottom reflecting mirror is enabled to be increased in optical path during reproduction in the process of advancing in the resonant cavity. The optical resonant cavity provided by the invention has different resonance conditions from a parallel plane resonant cavity, and can acquire small linewidth and a greater Q-value. In addition, the optical field energy can be effectively controlled within a certain area, and the diffraction loss is reduced.