The invention discloses a displacement sensor and a displacement measuring method. The displacement sensor comprises a conical displacement body, an LC resonance circuit and a resonance detection module, wherein the resonance detection module is used for detecting the resonance frequency of the LC resonance circuit; the conical displacement body penetrates through an inductance coil of the LC resonance circuit; the inductance coil of the LC resonance circuit moves along the central axis of the conical displacement body; the inductance coil moves to a start position and obtains the resonance frequency Dmin of the LC resonance circuit; the inductance coil moves to an end position and obtains the resonance frequency Dmax of the LC resonance circuit; the inductance coil moves to a test position, the displacement generated by the inductance coil is shown in the description, wherein H is the distance between the start position and the end position, D is the resonance frequency of the LC resonance circuit at the test position. According to the invention, the displacement is obtained by detecting the resonance frequency of the resonance circuit; the displacement sensor is simple in structure, stable in performance, simple and accurate in displacement calculation.