In this paper, a new kind of salt resistance, high temperature resistance, strong inhibition of drilling fluid loss agent SN-K is prepared with monomers AA, AM, AMPS and DMDAAC by aqueous solution polymerization, and the initiator system are (NH4)2S2O8 and NaHSO3. The best monomer molar ratio is produced by single factor experimental method and the molar ratio is n(AM):n(AMPS):n(AA):n(DMDAAC)=1:2:2:1. In addition, the optimum reaction conditions as follows: the reaction temperature and time are 65 ℃ and 4 h, the mass concentration of monomer is 20%, the adding amount of initator is 0.5%, and then KOH solution is used to adjust the pH value of reaction system, at the same time, the strong inhibition ion K is also introduced. It was found that the drilling fluid have a good fluid loss effect after a pretreatment of high temperature 180 ℃ and 16 h, when the adding amount of drilling fluid loss agent SN-K is 1.5%, in a such condition, the FLAPI is 6.5 mL. And then, the scroll shale recovery experiment shows that cuttings recovery is higher than the system of KCl. Additionally, the micro structure of HTHP filter cake is conducted by scanning electron microscopy (SEM), the results shows that the HTHP filter cake have a dense grid structure.