Provided are an FGFR4 inhibitor with the structure of formula (I) and a preparation method and use thereof. The series of compounds of formula (I) have a very strong inhibitory effect on the FGFR4 kinase activity, and have a very high selectivity; and the same can be widely used to prepare drugs for treating cancers, in particular, liver cancer, stomach cancer, prostate cancer, skin cancer, ovarian cancer, lung cancer, breast cancer or colon cancer, and it is expected that the same can be developed into a new generation of FGFR4 inhibitor drugs.