A method and apparatus for determining phase sensitivity of an accelerometer based on an analysis of the harmonic components of the interference signal, which can estimate phase lags of an accelerometer through an analysis of the interference signal obtained using a single photo-detector when the accelerometer moves in sinusoidal motion with an initial phase of vibration. The method comprises the steps of obtaining an interference signal in a time domain generated from a signal reflected by an accelerometer and a fixed mirror using a single photo-detector; transforming the interference signal in the time domain into a signal in a frequency domain including a plurality of harmonic signals by Fourier transform; and determining the phase sensitivity of the accelerometer using initial phase of vibration displacement of the accelerometer, which is included in the interference signal in the frequency domain.