Due to the special shape characteristic of a laser rod, the traditional double-pass test method, which has high sensitivity, tends to have obvious diffraction effect and edge black ring caused by multiple imaging. The result leads to the reduction of the effective measurement area, which has a negative impact particularly on the measurement of small aperture optical components. To avoid these problems, the wavefront aberration of laser rod is measured by the single-pass method. The right-angle prism is used as the reflection part to ensure the test light passes through the laser rod only once, so that the number of equivalent circular holes and the imaging times can be reduced. We use the expanded multi-hole model to discuss the diffraction effect and analyze the cause of edge overlap from the perspective of imaging to derive the advantages of the single-pass method. In addition, considering the matching of the reference light and the test light, it is necessary to rotate the right-angle prism by at least 5.40° to improve the contrast of the interferogram. Finally, the measurement result of the laser rod wavefront was as follows: the peak-valley value is 0.068λ and the root mean square is 0.012λ.