This application provides a measurement method, a terminal device, and an access network device. The measurement method includes: measuring, by a terminal device, signal quality of a plurality of beams, where the signal quality of the plurality of beams is obtained by using synchronization signal blocks; the signal quality of the plurality of beams includes signal quality of a same beam at different moments, and the plurality of beams belong to one cell; and obtaining, by the terminal device, signal quality of the cell based on the signal quality of the plurality of beams. In this way, cell measurement based on a synchronization signal is implemented, and the signal quality of the cell obtained based on the signal quality of the plurality of beams at the different moments is more accurate.