Fiber optic accelerometer receives more and more attention in recent years due to its advantages. A fiber optic accelerometer based on two-end fixed beam is presented, which is on the basis of the beam sensors. A kind of small-diameter single-mode optical fiber with high numerical aperture is wrapped on the beam as the sensing fiber. The minimum bending radius of the single-mode is analyzed, thereby more fiber can be affixed to the beam arm without any bending loss and the sensitivity is enhanced. The transverse sensitivity is greatly reduced due to the double- ended fixed structure which is convenient for the production of three- dimensional sensor. The nature frequency of the sensor and the sensitivity are analyzed theoretically. The linearity of the sensor response is analyzed by experiments. The sensor presented has the natural frequency around 360 Hz, and its sensitivity up to 3300 rad / g at 100 Hz. It can be used to detect low-frequency acceleration effectively.