Fiber optic acceleration sensors are important acceleration sensors,w hich are widely used in the national economy and national defense industries.In this paper,we present a micro-electro-mechanical system (MEMS)-based horizontal axis fiber-optic acceleration sensor,which can be integrated with t he Z-axis optical fiber acceleration senor to form a monolithic three-axis optical acceleration senor w hose optical fiber outlets are in the same direction.The sensing theory has been proposed and the MEMS acc eleration sensor chip has been fabricated and packaged successfully.The preliminary test results show that the sensitivity of MEMS-based fiber-optic acceleration sensor is 164mV/g,and the 3dB bandwid th is 1600Hz.