Abstract: To solve the problem of the high drag and torque in drilling extended reach wells and horizontal wells, to ensure operation safety and improve operation efficiency, based on sea-water polymer drilling fluid, an extreme-pressure lubricant using in drilling fluid, PF-EXLUBE was developed through screening and evaluating experiments of the properties of conventional lubricating and extreme-pressure of a series of lubraicants. The extreme pressure lubricator and the lubrication evaluation simulation device (LEM) were used to evaluate the lubricating properties of potassium chloride-polymer, saturated sodium chloride drilling-in fluid and potassium formate drilling-in fluid respectively.The experimental results show that when the amount of PF-EXLUBE is 1%, the friction coefficient is reduced by 33% ～95% under normal temperature conditions; the friction coefficient is reduced by 60% ～80% under high temperature and high pressure (150 ℃, 100 psi) conditions. PF-EXLUBE has been first applied in a well of the eastern South China Sea. The application results show that adding 2% PF-EXLUBE to the drilling fluid the torque of drilling could reduce by 15% ～20%, and the effect lasts for a long time. It shows good torque reduction effect.