The micro displacement experiment,which uses glass etching model to simulate the structure of rock pore,is an important means to study the distribution of remaining oil.The contrast of glass etching model is very low,which means it is hard to get a clear image of the ultra-low contrast pore-edges by using the macro lens and diffuse lighting.It needs to alter the lighting system to improve the contrast of the captured image in the premise of uniform illumination.By studying the effect of illumination light on image acquisition quality,this article designs a new illumination system based on transmissive Kohler illumination to significantly improve the contrast of the pore-edges in the acquired image.This article also derives the intensity distribution of Kohler illumination and discusses the influence factors of evenly distributed illuminance,and deduced the design basis of parameters in the lighting system to make the system′s illumination uniform.It is verified through experiment that the design of this paper is effective:the illumination distribution is uniform and the contrast of the acquired image is significantly enhanced.There lies a high promotional value of the new system.