Abstract: The present application discloses a single-frequency continuous-wave optical parametric oscillator, comprising a pumping source, a focusing lens, a resonant cavity, an optical parametric down-conversion crystal, and a birefringent crystal. The resonant cavity comprises a concave-convex lens, an output planoconcave lens, and at least two transitional planoconcave lenses; and a waist spot of pump light obtained through the focusing lens is located between the concave-convex lens and a first transitional planoconcave lens adjacent to the concave-convex lens on a light path. The center of the optical parametric down-conversion crystal coincides with a waist spot of the pump light; the birefringent crystal is located at the beam waist between the output planoconcave lens and the second transitional planoconcave lens adjacent to the output planoconcave lens on the light path; and the birefringent crystal adopts a critical phase matching or non-critical phase matching mode.