The invention discloses a thin-diameter solid-core polarization-maintaining photonic crystal fiber of a two-layer structure, wherein the cross section of an optical fiber is circular. The polarization-maintaining photonic crystal fiber sequentially and structurally comprises a coating layer, a quartz cladding layer, cladding air holes and a fiber core from outside to inside. The cladding air holes are divided into two layers. The first layer of air holes is composed of a first layer of big holes and a first layer of small holes. The second layer of air holes is composed of a second layer of big holes and a second layer of small holes. The circle center of the cross section of the optical fiber serves as an origin and the circle centers of air holes in the first layer are arranged in a regular hexagon shape with the circle center of the cross section of the optical fiber as the distribution center thereof. Two big holes are arranged in the first layer and the two big holes are symmetrically arranged in the transverse direction. Four small holes are arranged in the first layer and the four small holes are at the periphery of the first layer of air holes. The circle centers of air holes in the second layer are arranged in a regular hexagon shape with the circle center of the cross section of the optical fiber as the distribution center thereof. Two big holes are arranged in the second layer and the two big holes are symmetrically arranged in the longitudinal direction. Ten small holes are arranged in the second layer. According to the technical scheme of the invention, the geometrical size of the optical fiber can be greatly reduced. Therefore, the weight of the optical fiber ring is reduced. The size of an optical fiber ring is reduced, and the miniaturization of a gyroscope is facilitated. The integration degree of an optical fiber device is improved.