The present disclosure relates to signal transmission methods and apparatus. One example method includes receiving, by a terminal device, modulation and coding scheme (MCS) information sent by a network device, determining a modulation order used by the terminal device for data transmission, where the modulation order is determined based on the MCS information sent by the network device, information about a waveform used by the terminal device, and a preset correspondence between an MCS index and a modulation order, and transmitting data based on the determined modulation order.