This application relates to the communications field, and provides a transmission mode determining method and an apparatus, to better select a transmission mode and/or a transmission parameter of data autonomously. The transmission mode determining method includes: A first device measures a first resource set based on first information, to obtain a first measurement value, where the first information includes at least one of the following information: a subcarrier spacing of the first resource set, a quality of service parameter of first data, and feedback information between the first device and a second device, and the first resource set is to be used to transmit the first data. The first device determines a transmission mode of the first data based on the first measurement value, and/or determines a transmission parameter of the first data based on the first measurement value.