Abstract: The adjustment of light path of biprism interference is complicated，and there are many details for operating to notice，it is difficult for students to understand these details about experiment if teacher does not introduce and explain these details，and students often obtain abnormal experimental phenomena. Teacher presents the experimental principles through macro view，consciously heuristic students establish optical set-up，and finds out the origin of the abnormal experimental phenomena. Finally，teacher explains the abnormal experiment images. As a result，students can take the experiment process as a whole，and achieve experimental expectations.

Key words: biprism interference, ridges, virtual light source