A new type of real-time holographic three-slit interferometer is presented. It uses a calcite polarized optical element to obtain objective light and reference light to record a hologram. Its remarkable feature is to use a beam of fixed slit diffracted light as the reference light to record the lateral slit diffracted wave front, and to use also the same diffracted light as the illuminating light to reconstruct the wave front. This insures the phase distribution of the reconstructed wave front against the influence by the small natural direction drift of the laser beam and also by the tiny external vibration. The stability, reliability and measuring accuracy of this apparatus are improved notably. A new type of real-time holographic three-slit interferometer is presented. It uses a calcite polarized optical element to obtain an objective light and reference light to record a hologram. Its remarkable feature is to use a beam of fixed slit diffracted light as a reference. light to record the lateral slit diffracted wave front, and to use use the same diffracted light as the illuminating light to reconstruct the wave front. This insural the phase distribution of the reconstructed wave front against the influence by the small natural direction drift of the laser beam and also by the tiny external vibration. The stability, reliability and measuring accuracy of this apparatus are improved notably.