Active light measurement based on structured light is widely used in industrial measurement for its several advantages, while the Gamma nonlinearity, vibration, and noises easily lead to phase error and effect accuracy of three-dimensional measurement. Due to Gamma nonlinear problem for measurement system and different brightness distributions of projector, the system has different Gamma values. An image is projected on a standard whiteboard with smooth surface, and partitioned by using grayscale feature by histogram statistics. According to sub-regional information target area of the projector sub-area information is obtained to establish different regions modelling, which is used to compensate initial phase. To avoid system jitter and noise, original image is pre-processed before solving the phase. Applying this method to actual measurement, precision and accuracy of phase are greatly improved, and the method is simple and convenient, compared with existing methods of eliminating the nonlinearity of Gamma.