This application provides an uplink signal sending method and receiving method, a communications device, and a network device. The method includes: receiving, by a terminal device, downlink control information DCI sent by a network device; determining, by the terminal device based on the DCI, a transport block size TBS used for transmitting an uplink signal; and sending, by the terminal device, the uplink signal on two contiguous uplink subcarriers in a Pi/2 BPSK modulation mode based on the determined transport block size. Therefore, the uplink signal is transmitted in the Pi/2 BPSK modulation mode by using the determined transport block size.