In this study, a new method for visualization of oil film flow is proposed. This method is expected to reduce oil consumption in an engine clearing behaviors of lubricating oil. We are aiming to visualize them by dissolving a photochromic dye in lubricating oil and coloring with UV rays. This paper explains the methods of improving signal-to-noise ratio and the application to flow visualization. Firstly, we examined the suitable concentration of a photochromic dye for the purpose of increasing colored species. As a result, we found that 0.4% is the suitable concentration for the spiropyran-ester oil solution. We also measured the color fading reaction under the different temperature conditions and confirmed that a high signal state of the colored solution exists at a moment after colored with UV laser regardless of the oil temperature. Secondly, we quantified the relation between color density and intensities of UV rays. Consequently, it was confirmed that the increasing energy density of UV rays is effective in improving color density. Finally, flow visualization was tried in the complex shape flow channel made thickness approximately ten micrometers. The test oil flowing through this channel was colored with a focused third harmonic of YAG laser. The distributions of flow velocity and supplied oil to the channel were visualized with this method.