An iterative algorithm for multiple incoming wavelengths is proposed to design a computer-generated holographic diffuser with the features of high light utilization efficiency and uniform color mixing. The amplitude transmittance of this computer-generated holographic diffuser is constant, while the phase transmittance consists of multiple phase levels. This diffuser is designed according to the Fraunhofer diffraction theory and can uniformly spread the different input light at the same time. The simulation results show that over 88% average far field amplitude transmission efficiency is achieved for each input light and the output uniformity is within 12.4%.