Carrageenan (KC) was grafted onto aluminum tripolyphosphate (ATP) to achieve new modified filler (KC-ATP), and then KC-ATP was added into waterborne epoxy (WEP) to prepare anticorrosive composite coatings. The morphology and structure of ATP before and after modification were characterized by FTIR, XPS, TG and SEM. The results showed that KC was successfully grafted onto the surface of ATP, which improved the water solubility of ATP. The corrosion resistance of the composite coatings was investigated via electrochemical impedance spectroscopy (EIS) and salt spray test. The results revealed that the anticorrosive property of composite coatings was obviously superior to that of neat waterborne epoxy coating, and the corrosion resistance of composite coating was best when adding 1.0% (based on the quality of waterborne epoxy resin, the same below) KC-ATP functional pigment. The polarization resistance Rp of the coating after being immersed for 48 hours is 8.183×107 Ω∙cm2, which is much higher than those of ATP modified composite and pure epoxy coatings.