In the process of high temperature deep well drilling，water based drilling fluid is prone to problems such as sharp increase in fluid loss and deterioration of performance，which seriously affects wellbore stability and drilling safety. Therefore，the research on high temperature fluid loss control mechanism and materials has become a critical issue in current oil and gas drilling engineering. This review summarizes the influencing factors and mechanism of high temperature fluid loss of water based drilling fluids，analyzes the synergistic effects of temperature，pressure，and formation conditions on leak off performance，and reveals the underlying mechanisms of clay particle aggregation，polymer molecular chain degradation，and mud cake structure disruption under high temperature conditions. On this basis，the research progress of high temperature fluid loss control materials in recent years is discussed，including the functional design，synthesis methods and performance optimization strategies of modified natural polymers，high temperature polymers，sulfonated materials，and nanocomposite materials. The high temperature stability and fluid loss control effect of four kinds of fluid loss reducer are compared. The problems of ultra-high temperature adaptability，environmental protection and economy are summarized，and the future development directions of extreme environment resistance，green sustainability and intelligent design synergy are prospected. This review provides theoretical insights and technical support for the development and application of fluid loss control materials for high temperature drilling fluids.

One of the main reasons for rheology out-of-control of high density water-based drilling fluid is the increase of inferior solid phase content. Inferior solid phase is dispersed in high density water-based drilling fluid，which enhances the system architecture，resulting in increased drilling fluid viscosity and higher shearing force. Based on the principle of viscosity reduction by competitive adsorption，WNTHIN，a low molecular weight polymer viscosity reducer was synthesized with 2-acrylamide-2-methylpropanesulfonic acid，styrene，maleic anhydride，N and N-dimethylacrylamide in a molar ratio of 1∶2∶1∶1.Test results of the viscosity reducer show that WNTHIN can significantly reduce the viscosity and shearing force of high density potassium polysulfonate water-based drilling fluid with a density of 2.40 g/cm³，with plastic viscosity reduced by 42.85%，static shearing force reduced by 51.35%，and the recommended WNTHIN dosage addition is 1.5%. The field application of WNTHIN in a well in Penglai Gas Field showed improved rheology of high density potassium polysulfonate water-based drilling fluid. The plastic viscosity dropped from 58 mPa·s to 30 mPa·s，the yield point dropped from 29 Pa to 14 Pa，and the 10 min static shearing force dropped from 28 Pa to 16 Pa. The performance of the high density water-based drilling fluid has been improved to meet the technical requirements for safe drilling in deep wells.