A new kind of synthetic cation water based lubricant was prepared through selecting suitable synthetic base oils,additives and emulsifiers,in order to decrease the torque and pressure drop of the extended reach wells in the oilfield more effectively,and to meet the demand of geologic control and environmental protection.The extreme pressure additives selected can form absorption film and chemical reaction film on the surface of the formation and drill tool,the cationic surfactant selected as the emulsifier can improve the solubility,and enhance the absorbability through positive electricity absorption.The test results show that the fluorescence level of the synthetic cation water based lubricant is lower than 4.This lubricant can match perfectly with the drilling mud,which can decrease the damping coefficient by 74%,reduce the torque by10%,and decrease the extreme pressure lubrication coefficient by more than 75%.The results by fourball tester show under high load,this lubricant has quite high oil film strength and long term extreme pressure resistance,which can meet the demand of extreme pressure and antiwear in the extended reach wells.