The invention discloses an optical interferometer used for detecting the inner surface of a hollow cylinder. The inner surface is located on the inner side or the outer side in the circumferential direction of the hollow cylinder, a condensation convex lens of the inner surface is located between a laser and a collimation convex lens, and the focus of the condensation convex lens and the focus of the collimation convex lens coincide; a beam splitter located between the condensation convex lens and the collimation convex lens is used for dividing light of an auto-collimation convex lens into a first light beam and a second light beam; a standard optical flat is located on one side, back to the beam splitter, of the collimation convex lens, the surface, facing the collimation convex lens, of the standard optical flat is a convex surface, and the surface, back to the convex surface, of the standard optical flat is a standard reference surface; a conical reflector is located in the hollow cylinder to be detected, and a rotary shaft of the conical reflector, the axis of the hollow cylinder and the axis of the standard optical flat coincide. According to the optical interferometer, feature information of the inner surface in the whole stereoscopic hollow cylinder can be obtained at a time, and test efficiency, accuracy and reliability are also greatly improved.