A system and method includes: sending a channel state information-reference signal CSI-RS to a second terminal device, where a frequency-domain bandwidth of the CSI-RS is the same as a frequency-domain bandwidth of a resource pool, the resource pool is a time-frequency resource set included in a sidelink SL bandwidth part BWP, the resource pool includes one or more consecutive sub-channels in frequency domain, one sub-channel in the resource pool includes one or more consecutive physical resource blocks PRBs, and the resource pool is determined based on a periodic bitmap in time domain. According to the method and apparatus in the embodiments of this application, a first terminal device can obtain channel state information CSI of each sub-channel in the resource pool, and allocate a resource based on the CSI of each sub-channel in the resource pool, improving a communication capacity in an SL scenario.