With the development of manufacturing technology, the three-dimensional optic measurement technology is developed rapidly. Projection measurement with two cameras is a new kind of optical measurement technique. In the measurement process, the measurement space can be got by the phase value. In order to get high precision measuring phase for the technique, a phase-shifting method is proposed with Gray code. The method can calculate the phase value by projected phase transfer function and irradiance function of projected structural light. The non-sinusoidal, non-periodical effects of projected structural light are considered. The precision of strip and phase is improved by the method. The result precision of phase can reach sub-pixel by interposition.