An uplink data transmission method and apparatus are described. The uplink data transmission method includes receiving a first message including transmission mode information. The transmission mode information indicates that a terminal device is capable of transmitting uplink data by using at least two contention transmission units (CTUs) that are in a same transmission time interval (TTI). The CTU refers to a transmission resource combining: a time, a frequency, and a code domain; a transmission resource combining a time, a frequency, and a pilot; or a transmission resource combining a time, a frequency, a code domain, and a pilot. The uplink data transmitted by using the at least two CTUs is partially the same or totally the same. The method further comprises the terminal device sending a second message including indication information, where the indication information is used to enable the terminal device to determine, according to the indication information, a CTU for uplink data transmission.