An embodiment method includes: obtaining, by a first device, at least one parameter used to determine transmit power; determining, by the first device, the transmit power according to the at least one parameter; and sending, by the first device, data by using the determined transmit power. The at least one parameter includes at least one of the following parameters: a resource pool used for data transmission, a type of a to-be-sent message or service, a transmit interval or a transmit frequency of a to-be-sent message or service, a size of a message packet, a priority of a to-be-sent message or service, an ID of a to-be-sent message or service.