Alignment and testing of optical axis parallelism are the key problems in alignment of a multi-optical axis system. We propose a method which can adjust optical axis parallelism and single-channel wavefront aberration simultaneously in multi-axis imager. Firstly, the imager's installation base surface is adjusted to be perpendicular to the optical axis of the interferometer and remain motionless precisely by using theodolite. Then, according to the measurement principle of wave aberration with interferometer, each channel axis is adjusted to be parallel to the axis of the interferometer. While imaging quality in each channel is measured, alignment on each channel axis parallelism is accomplished. By this method, three-axis parallelism in annular three-channel imager is aligned. The accuracy of axis parallelism is up to 15″, and the imager requirement (30″) is satisfied. Feasibility and precision of this method are verified.