Aim\ Explaining which information of acceleration are included in the output signal of an accelerometer. Methods\ Deducing analytic formula of its output signal according to the physical model of an accelerometer. Results and Conclusion\ There are four types of information as follows in the output signal of an accelerometer: the acceleration of the centre of mass of moving object; vibration accelerations caused by the position of the accelerometer fixed versus the centre of its mass; the response of on acceleration the structured part fixing the accelerometer and the response of the accelerometer on excitation.