Unconventional oil reservoir has presented the potential to become a significant source of hydrocarbon in the future productions. Many shale oil systems consist of nano-scale pores and micro-scale fractures that are significantly smaller than those from conventional reservoirs. Such small size of the pore throats in shale may differ from the size of the saturating fluid molecules by only slightly more than one order of magnitude. This difference will result in different wettability, fluid flow mechanisms and storage capabilities in unconventional shale oil systems. However, the fluid flow behavior in the micro-scale or even nano-scale pores and channels is poorly investigated and understood. Therefore, it is increasingly important to investigate fluid flow behaviors and the fluids residue saturation in the nano-scale channels. In this work, a lab-on-chip approach for direct visualization of the water/oil flow in nano-scale channels is developed by using advanced confocal microscopy system combined with nano-fluidic chip. A comprehensive study of water/oil flow behaviors is presented. During drainage process, liquids tend to be piston like flow under micro; both residual phase saturation and configuration affect the flow behavior under smaller scale. During imbibition process, a fading out phenomenon was observed which. For residual phase saturation, confocal system can give a precise description within 3-dimensional scale.