The present invention relates to an FGFR4 inhibitor having a structure represented by formula (I), preparation method therefor, and applications thereof. A series of compounds represented by formula (I) in the present invention have very-strong inhibition effect on the activity of FGFR4 kinase, have very-high selectivity, can be widely used in the preparation of drugs for treating cancers, specially a liver cancer, a stomach cancer, a prostate cancer, a skin cancer, an ovarian cancer, a lung cancer, a breast cancer or a colon cancer, and can be developed into a new-generation FGFR4 inhibitor drug.