The ancient buried hill in Jiyang Depression has the characteristics of complex geological structure and deep burial, but it is potentially rich in oil and gas resources. Due to the poor rheological performance and high temperature stability of drilling fluids, the reservoir damage, sand sticking, lost circulation occurred frequently during the early stage of drilling the ancient buried hill reservoirs. In order to solve drilling fluid problems in ancient buried hill reservoir, the high temperature rheology modifier (HTRM-1) was firstly developed through the micellar polymerization of N-vinyl pyrrolidone (NVP) ,2-acrylamide-2-methylpropanesulfonic acid (AMPS) and divinylbenzene ( DVB) . According to the evaluation results, HTRM-1 exhibited with high temperature resistance up to 160℃ , and the ratio of plastic viscosity and yield point of 2% aqueous solution was 1 . 05. Furthermore, the clay-free water-based drilling fluid ( SFDF) was finally established with temperature resistance of up to 160℃ , the ratio of plastic viscosity and yield point of 0. 42, HTHP filtration of 9. 6mL, and the core permeability recovery was 93. 13% . It was proved from the field tests that SFDF fluids displayed stable rheological and filtration control behavior and it also exhibited good reservoir protection properties, which could provide technical support for the exploration and development of buried hill reservoirs in Shengli Oilfield.