Abstract: In view of great viscosity in high density drilling fluid system, rheology behavior is difficult to regulate and control, down hole problems emerges frequently. By means of optimizing polymer flocculant, bentonite content, lubricant, inhibitor, the best formula of high density drilling fluid system with low clay phase is defined and a suit of high density drilling fluid system with low clay phase is developed. Laboratory study results demonstrated that the drilling fluid system has good potential resistance to cuttings, NaCl and gypsum contamination, good inhibition and formation sealing ability, and cuttings rolling recovery achieves 93.7% . The drilling fluid system can satisfy the drilling technology demands of high temperature and high pressure, strong mud-making, high penetration rate and mature micro-fissure development.