Abstract: The physicochemical structure of mud cake is the intrinsic factor controlling the quality of mud cakes,and fewer studies on the spatial distribution of the physicochemical structure of mud cakes have been conducted than the studies conducted on the surface microscopic morphology and element composition of mud cakes.A new method of studying the spatial distribution of the physicochemical structure of mud cakes using fluorescence microscope and the software Adobe Photoshop CS6 is presented.By measuring the pixels of the white (the original bluefluorescence) area and calculating their ratio,the concentration distribution of the tested additive in different layers of the mud cake can be seen directly.Using this method,a self-made compound (polymeric and nano) material,LX-2,was studied.The studies have demonstrated that the fluorescent area of polymers found in mud cakes takes on a spatial distribution of "surface layer >intermediate layer >bottom layer".The quantity of adsorbed water of mud cake measured with conventional drying method and polymer content in the mud cake measured with incineration method all take on a similar spatial distribution such as that just mentioned.It is believed that addition in drilling fluids of deformable additives that still retain strong hydration capacity and strong colloid-formation capacity,and effectively render mud cakes water-absorptivity at elevated temperatures,high pressures and high salinity conditions,will be an important way of enhancing the quality of mud cakes.This new method will help in further understanding the spatial distributioncharacteristicsof the physicochemical structure and its effects on the wall building capacity of drilling fluids,and this in turn,provides a new perspective and basis of improving the wall building capacity of drilling fluids.