As the exploration and development of Tuha Oilfield gradually advances toward deeper and more complex areas，the well site deployment is approaching environmentally sensitive farmland and forest. In order to ensure the safe drilling of deep wells，higher technical requirements are proposed on environment protection，high temperature resistance and handling capacity of downhole complex issues and anomalies of drilling fluids. Considering factors such as wellbore stability，wellbore cleanup，and reduction of friction and resistance，researches were conducted in terms of the drilling fluid performance of inhibition，plugging，lubrication and environment protection. Through the laboratory experiments to optimize the desulfonation degradable high temperature resistant treatment agent and system composition，a high temperature environmentally friendly drilling fluid system was derived from the composite salt drilling fluid formula. As shown in laboratory testing，the drilling fluid has stable performance at 160 °C，with the EC₅₀ of 5.1×10⁴，and is non-toxic with the heavy metal content complying with the national ecological environment discharge criteria. The HTHP fluid loss is less than 10 mL，the mud cake drag coefficient is 0.043 7-0.052 4，the yield point is greater than 12 Pa，and the shale rolling recovery rate is 95.36%. The high temperature environmentally friendly drilling fluid system has been successfully applied in Well Jixin-6. The drilling of the whole well is smooth with no complex issue，creating a new record of the deepest vertical depth of the Jixin-1 Block and sufficiently proving that the drilling fluid system has good performances of inhibition，plugging，cutting-carrying and lubrication.