Provided are an eyepiece and a head-mounted display device, where the eyepiece includes: a positive lens and a negative lens arranged sequentially and coaxially; where a light incident surface of the positive lens is a planar Fresnel surface, and a light emergent surface of the positive lens is a convex surface; a light incident surface of the negative lens is a concave surface, and a light emergent surface of the negative lens is a convex surface; and the light to be observed is incident on the light incident surface of the negative lens and refracted by the negative lens to the light incident surface of the positive lens, and enters human eyes after being refracted by the positive lens. The eyepiece and head-mounted display device provided by the present disclosure realize an ultrathin eyepiece optical system and facilitate a miniaturized and lighter head-mounted display device.