Provided are an FGFR4 inhibitor having the structure of formula (I), and a preparation method therefor and the use thereof. The compound has a very strong inhibitory effect on FGFR4 kinase activity and has a very high selectivity, and can be widely used in the preparation of a drug for treating cancers, especially prostate cancer, liver cancer, pancreatic cancer, esophageal carcinomas, gastric cancer, lung cancer, breast cancer, ovarian carcinomas, colon cancer, skin cancer, glioblastomas or rhabdomyosarcomas, and is expected to be developed into a new generation of FGFR4 inhibitor drugs.