Abstract: In deep well drilling, hole collapsing is likely to take place in some intervals, thus the drilling fluid systems are required to posses better inhibition capacity, better lubricity and higher temperature tolerance. A fluorescence free anti-sloughing filtrate reducer KH-931 is developed to meet these requirements, as it has the following advantages over good shale hydration and dispersion controlling capability, lower filtration, higher temperature tolerance and better compatibility with other additives. Drilling fluid treated by it is stable and easy for maintenance, and suits for drilling in the sloughing intervals. In addition, as it is free of fluorescence and causes little interference to mud logging, it is a better alternative for drilling the exploratory well and evaluation well.