PFL series polymer filtrate reducer is characterized of low viscosity,good capacities of depressing the filter loss,heat resistance and salt tolerance.The apparent viscosity of 1% PFL-L aqueous solution and 1% PFL-H aqueous solution were 12 mPa · s and 26 mPa · s,respectively.After aging at 240℃/16 h,with the addition of 5%PFL-L,the filer loss(FL) of the saturated salt water mud(SSWM),composed of 4% bentonite and 36% NaCl,decreased from 226 mL(blank group) to 32 mL;with the addition of 4%PFL-H,the FL of the SSWM decreased from 226 mL(blank group)to 8.2 mL;with the addition of 1.5% PFL-H,the FL of fresh water mud,composed of 4% bentonite,decreased from 100 mL(blank goup)to 9.6 mL.Based on the PFL series ultra-high temperature polymer filtrate reducer and the optimized sulfonating filtrate reducer,inhibitor,lubricant,thinner,the strong inhibited brine and fresh drilling fluids,which were heat resistant to 200℃,were formed.The field application manifested that the PFL series ultra-high temperature polymer filtrate reducer showed strong heat resistance and good capacities of depressing the filter loss,making sure that the Xuwen X3 well was drilled to 6010 m and the logging temperature of 211℃ at the depth 5974 m.