This application provides a bandwidth part switching method, an apparatus, and a system, and may be applied to a non-terrestrial network NTN, to implement BWP switching based on multi-color frequency division multiplexing, and reduce signaling overheads in a BWP switching process. In the method, a terminal device may report, in a second BWP to a network device, an index of a first SSB whose signal quality is greater than or equal to a first threshold in one or more SSBs in a first BWP, and switch from the second BWP to a third BWP. The one or more SSBs correspond to at least one BWP other than the first BWP, and the third BWP is a BWP that is in the at least one BWP and that corresponds to the first SSB. After receiving the index of the first SSB in the second BWP, the network device determines the third BWP, and performs service data transmission with the terminal device in the third BWP.