Abstract: For permanent downhole microseismic monitoring of unconventional hydrocarbon reservoirs, we develop a type of three-component fiber MEMS geophone installed outside the casing pipe based on the Fabry-Pérot (F-P) interference principle and micro-electro mechanical system (MEMS). The instrument converts microseismic signals into F-P cavity length variations, and fast demodulation is accomplished using ultrafast spectroscopy and dynamic white light interferometry. We design and theoretically simulate MEMS accelerometer chip with the sensitivity of μm/g-scale, the samples of which are fabricated using double-side exposure process. The external diameter of 25mm is achieved through highly integrated miniature structure design, non-gel encapsulation technology, and ceramic micro-machining for permanent installation outside the casing pipe and high-precision detection at high temperatures. According to performance testing conducted using the new geophone and standard electronic accelerometer in the lab, the new geophone shows resistance to high pressure of 175 MPa and high temperature of 180 ℃, sensitivities of 1.2382, 1.2590, and 1.0862 μm/g, respectively, operating band of 0~350 Hz, measuring range of ±5 g, linearity error < 0. 01%, and transverse crosstalk resistance < 5%. Owing to good performance of high temperature and high pressure resistance, small size, high sensitivity, and good linearity, the new geophone will play an important role in fracturing stimulation of unconventional reservoirs and hydrocarbon production.