In order to improve the protective properties of carbon fiber/epoxy composites，reduce their water absorption，and prolong the service life of the composites，poly-tetrahydrofuran-ether-glycol（PTMG） with different relative molecular masses was used to modify epoxy resin，and a high-performance modified resin was designed and synthesized as a film-former，and protective coatings for composites were prepared. At the same time，the pigment/binder ratio of the coatings was further regulated，and the properties of the coatings such as weather resistance，adhesion，water resistance and flame retardant were systematically
studied. The results showed that when the mass ratio of PTMG with 800 molecular weight and PTMG with 2 000 molecular weight was 1. 5，the properties of the modified resin reached the best state. When the coating pigment/binder ratio was 1. 1，the prepared coating had good environmental resistance and water resistance，the water absorption rate was as low as 0. 6%，the oxygen index was 25. 8%，and the adhesion by pulling method could reach 25. 33 MPa， which could provide good protection ability for composite materials，and had broad application prospects.