In order to solve the problem of poor temperature resistance of hydroxypropyl starch （HPS） ，a type of environmental-friendly filtrate reducer ，HPS was prepared by the reaction of corn starch and propylene oxide in alkaline solution， the optimal reaction was probed and the relation between molar substitution degree（MS）and filtrate reducing performance of HPS was studied，and the performance of the complex system composed of HPS and several viscosity reducers was investigated. The optimum reaction conditions were as follows：reaction temperature was 60℃ ，reaction time was 20 h，the amount of propylene oxide was 26%（based on the starch mass），the amount of sodium hydroxide was 0.7%（based on the starch mass），and the starch slurry mass fraction was 45%. The filtrate reducing performance of HPS was the best when MS was 0.23. HPPS was obtained through mixing silicon-fluorine type viscosity reducer GE with HPS at mass ratio of 0.5∶1，and HPPS could resist high temperature up to 150℃ in 4% NaCl salt water muds，whose viscosity was 16 mPa·s at room temperature. Compared with HPS，at the temperature of 140℃，HPPS could resist salt，Ca2+ and Mg2+ was up to 15%，900 mg/L and 360 mg/L，respectively.