In order to eliminate the influence of the gamma nonlinearity of the projector on the phase, this paper proposes a method to remove the gamma nonlinearity based on the eight-step phase shifting. The mathematical analysis and derivation of the phase are demonstrated, and the mathematical model is established between phase and projector gamma. For the gamma nonlinearity error within the four order of the projector, we illustrate that the expression of the phase is independent of the gamma nonlinearity. The experimental results show that the method can effectively reduce the phase error caused by the gamma nonlinearity. The standard deviation of the phase error is reduced to 8.3% of it. Besides, the standard deviation is reduced to 20.5% of it. This method is simple, reliable and universal, and it is not affected by ambient light and system parameters.