自准直法测薄凸透镜焦距实验中会出现多个干扰像，其中包括凸透镜后表面反射成像. 实验发现，通过调控凸透镜和平面镜的位置，可以得到等大倒立的干扰实像，但其亮度明显弱于自准直法成的像. 本文通过多次成像过程分析，给出了此干扰像的成像原理. 

Several interferential images are shown in the experiment of measuring the focal length of thin convex lens by auto-collimation method, including the direct reflection imaging of the rear surface of convex lens. It is found that an isometrical and handstand interferential real image is obtained by adjusting the position of convex lens and plane mirror. However, the brightness of the interferential image is weaker than that of the image achieved by auto-collimation method. In this paper, the imaging principle of the interferential image is explained by analyzing the multiple imaging process.