The invention provides a method and an apparatus for acquiring a displacement signal by an acceleration signal, so as to effectively solve the problem that vibration displacement is hard to acquire in most mechanical structures. Along the vibration of a mechanical structure, an acceleration sensor is arranged at an exciting end, an initial vibration acceleration signal is acquired, trend removal is carried out on the initial vibration acceleration signal, a first vibration acceleration signal with no trend is obtained, the first vibration acceleration signal with no trend is subjected to filtering, quadratic integral, and quadratic trend removal calculation and then is converted to a corresponding non-trend displacement signal, a simulation model is built if verification is needed, the displacement signal is added to the exciting end, a second vibration acceleration signal is outputted, the first vibration acceleration signal and the second vibration acceleration signal are compared, and when the two signals are consistent in a time domain and a frequency domain, the non-trend displacement signal is used for replacing the displacement signal for further application. Through a method of combining the test and computer simulation, the vibration displacement is acquired indirectly, and the method has the advantages of being simple and easy to operate, wide in application, high precision and the like.