In order to obtain starch filtrate reducer with good temperature resistance，a composite modified starch filtrate reducer（CCMS）was prepared by using corn starch as raw material，chloroacetic acid as carboxymethylation agent and epichlorohydrin as cross-linking agent. The structure of CCMS was characterized by infrared spectrometry，and the filtration reduction property，temperature resistance and salt tolerance of CCMS were studied. The results showed that CCMS had excellent filtration reduction property. The API filtration loss of base slurry decreased with increasing concentration of CCMS，and that increased with increasing salt dosage in base slurry. When the dosage of CCMS was 1.5%，the API filtration loss of freshwater-base slurry，4% salt water base slurry and saturated brine base slurry was 6.8，7.8 and 8.6 mL respectively. CCMS had good temperature resistance at 160℃. In freshwater-base slurry containing 40% CaCl₂，CCMS still had good filtration reduction property，and the API filtration loss of base slurry was 9.1 mL. CCMS could obviously increase the temperature resistance as well as high-temperature and high-pressure filtration reduction property of PLUS/KCl drilling fluid，which had similar characteristics with the same products abroad.