In order to study moment invariants of color image,the quaternion radial moments for describing color image are introduced,which can be seen as the generalization of traditional radial moments for gray-level image.Then,the affine invariants based on quaternion radial moment are derived.Adopting quaternion to color image processing can represent the color image in a holistic manner and parallel processing the R,G and B components.Experimental results show that the stability of our method is superior to L.V.Gool′s color affine moment invariants,and the value of σ/μ can improve one order of magnitude.The proposed quaternion moment invariants could be a useful tool in color pattern recognition task.