This application provides a data transmission method and apparatus. The method includes: obtaining, by a terminal, information used to indicate a first condition; obtaining to-be-transmitted data; and when the first condition is met, sending, by the terminal over a sidelink, the to-be-transmitted data that is on a first logical channel by using a first carrier frequency and the to-be-transmitted data that is on a second logical channel by using a second carrier frequency. In this method, the same data is sent, over the sidelink, on different carrier frequencies by using two logical channels, and a receiving device can receive the same duplicate data, thereby improving data transmission reliability.