Abstract: In order to study the problem of calculating phase shifts in the phase-shifting digital holography,the recording and reconstructing principle of phase-shifting off-axis lenless Fourier transform digital holography was analyzed based on the Fresnel diffraction and holographic theory.Then the complex field expression of four-step phase-shifting digital hologram based on arbitrary phase shifts was deduced.A new method was proposed to calculate arbitrary phase shifts by means of phase subtraction.The experimental results show that compared with the conventional method of four-step phase-shifting,it is not necessary to calibrate phase-shifting devices strictly with this method.The zero-order diffraction and the conjugate image are also eliminated effectively and the ratio of signal to noise is similarly improved.Therefore,the method contributes to the reduction of the complicacy of the measure system and the promotion of the development of four-step phase-shifting digital hologram.