In the field of wireless communication technologies, method and apparatus for determining a transport block size (TBS) of a data channel are provided. In a communication network, a terminal device receives control information from a network device. The control information includes modulation indication information and resource information of the data channel. The terminal device determines a modulation order and a code rate according to the modulation indication information, and determines number of time-frequency resources according to the resource indication information of the data channel. The terminal device determines the TBS according to the modulation order, the code rate, and the number of time-frequency resources. Based on the determined TBS, the terminal device decodes the data channel carried on the time-frequency resources or sends the data channel on the time-frequency resources.