An uplink signal sending method, comprising: 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 TBS; wherein the DCI comprises index indication information and resource unit quantity indication information, and the index indication information is used to indicate an MCS index; and the determining, by the terminal device based on the DCI, a TBS used for transmitting an uplink signal comprises: determining, by the terminal device, a TBS index based on the index indication information and a first mapping relationship, wherein the first mapping relationship is used to indicate a relationship between the MCS index, a modulation mode, and a TBS index; and determining, by the terminal device based on the TBS index and the resource unit quantity indication information, the transport block size used for transmitting the uplink signal, wherein the first mapping relationship comprises a first part and a second part, the first part is used to indicate a relationship between an MCS index, a QPSK modulation mode, and a TBS index, and the second part is used to indicate a relationship between an MCS index, the Pi/2 BPSK modulation mode, and a TBS index; and the second part comprises S TBS indexes, and/or a maximum value of a transport block size in the second part is 936 or 1000, wherein S is a positive integer, and S is greater than 2 and less than or equal to 5. 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 TBS; wherein the DCI comprises index indication information and resource unit quantity indication information, and the index indication information is used to indicate an MCS index; and the determining, by the terminal device based on the DCI, a TBS used for transmitting an uplink signal comprises: determining, by the terminal device, a TBS index based on the index indication information and a first mapping relationship, wherein the first mapping relationship is used to indicate a relationship between the MCS index, a modulation mode, and a TBS index; and determining, by the terminal device based on the TBS index and the resource unit quantity indication information, the transport block size used for transmitting the uplink signal, wherein the first mapping relationship comprises a first part and a second part, the first part is used to indicate a relationship between an MCS index, a QPSK modulation mode, and a TBS index, and the second part is used to indicate a relationship between an MCS index, the Pi/2 BPSK modulation mode, and a TBS index; and the second part comprises S TBS indexes, and/or a maximum value of a transport block size in the second part is 936 or 1000, wherein S is a positive integer, and S is greater than 2 and less than or equal to 5. determining, by the terminal device, a TBS index based on the index indication information and a first mapping relationship, wherein the first mapping relationship is used to indicate a relationship between the MCS index, a modulation mode, and a TBS index; and determining, by the terminal device based on the TBS index and the resource unit quantity indication information, the transport block size used for transmitting the uplink signal, wherein the first mapping relationship comprises a first part and a second part, the first part is used to indicate a relationship between an MCS index, a QPSK modulation mode, and a TBS index, and the second part is used to indicate a relationship between an MCS index, the Pi/2 BPSK modulation mode, and a TBS index; and the second part comprises S TBS indexes, and/or a maximum value of a transport block size in the second part is 936 or 1000, wherein S is a positive integer, and S is greater than 2 and less than or equal to 5.