The invention relates to the communication field and discloses a method for sending data in a relay system. The method comprises the steps as follows: service information to be sent is processed to obtain a first symbolic stream and a second symbolic stream; the first symbolic stream and the second symbolic stream have different reliabilities; a base station sends the first symbolic stream; a relay station receives the first symbolic stream and generates a third symbolic stream according to the first symbolic stream; the third symbolic stream and the second symbolic stream have the same reliability; after the base station sends the first symbolic stream, the base station sends the second symbolic stream after a period of time; and the relay station sends the third symbolic stream at the same time. The invention also discloses a base station, a relay station and a terminal. By adopting the technical proposal provided by the invention, the service information to be sent is processed into the symbolic streams with different reliabilities and the symbolic streams is sent at different moments, thereby avoiding sending same data twice and saving wireless resource of a system.