A method including determining, by a first terminal device, a size of a sidelink data packet, determining, by the first terminal device based on the size of the sidelink data packet, a first quantity of time-frequency units corresponding to the sidelink data packet, determining, by the first terminal device, a frequency domain resource of a second time-frequency resource from a first time-frequency resource, based on the first quantity, a resource selection rule, and at least one of a time domain resource of the second time-frequency resource, or a frequency domain resource of the second time-frequency resource, and performing, by the first terminal device, at least one of sending the sidelink data packet to a second terminal device on the second time-frequency resource, or receiving the sidelink data packet from a second terminal device on the second time-frequency resource.