Corruption of texture features of iris often occurs during denoising an iris image because of its irregularity and frangibility. So it is difficult to design iris image denoising algorithm. In this paper a novel iris image denoising algorithm is proposed, in which phase preserving principle is held to avoid corruption of iris texture features .Importance of phase information for iris image is shown by an experiment and the method to implement phase preserving by complex Gabor wavelets is explained. To verify the algorithm, white noise is added to iris images and Hamming distances between the iris images are calculated before and after the denoising algorithm is applied. The results show that the denoising algorithm can improve the quality of iris image evidently.