Abstract: Considering the complicated conditions of Block M in the cooperation area between CNOOC and Burma, such as the high formation porosity pressure and caving pressure, technical research of high density drilling fluid is conducted, as well as the technical difficulties are analyzed. The drilling fluid formulation is optimized, on the basis of the research on its bentonite content, inhibitor, weighting material, and sedimentation stability. Barites and ground iron ore are selected for weighting materials. Experimental results show that the optimized high density drilling fluid features in good rheological property, sedimentation stability and rejection capability. The high density drilling fluid technology has been applied to RM19-3-1 well successfully.