Embodiments of the present invention disclose a method, an apparatus, and a system for sending and receiving service data, where the method includes: first, obtaining, by a sending end, a target modulation mode different from a current modulation mode; and then, generating, by the sending end, invalid data, and temporarily storing service data at the same time; and then, performing encapsulation and mapping on the invalid data, switching the current modulation mode to the target modulation mode, modulating encapsulated and mapped invalid data according to the target modulation mode, and sending modulated invalid data to a receiving end; and finally, after the sending end completes the encapsulation and mapping on the invalid data, performing encapsulation and mapping on the temporarily stored service data, modulating encapsulated and mapped service data according to the target modulation mode, and sending modulated service data to the receiving end.