Waveguide multiplayer optical memory is a kind of new 3D optical memory based on new principle, and it can read the data by utilizing the effect of light scattering of waveguide defect. So how to measure the light scattered from the information pit is key technique which must be dealt with. This paper introduces the experimental principle of measuring the scattering light from the signal information pit by using the technique of optical conjugation, and presents the experimental result of scattering light measured by photomultiplier. The elementary experiment results prove that this experiment set can detect and measure the change of the scattering light when there is a information pit or not,and the length of the information pit which is measured in this experiment is corresponding with the theory value.