A digital phase shifting technique capable of quantitatively determining the phase of holographic interferometric fringes is presented. This technique uses computer control to take data and to calculate phase. The phase value at each detector point can be calculated by taking four successive intensity data frames with the reference phase shifted between each frame. The amount of phase shift introduced by this technique is unimportant. Theoretical analysis and experimental systems are described. Experiments are made in beam deflection measurements, holographic nondestructive testing and surface contouring of diffuse object to show the versatile applications of this technique.