The present invention discloses an uplink data transmission method, a terminal device, and a network device. The method includes: sending, by a terminal device to a network device, information used to request a grant-free transmission resource; receiving, by the terminal device, resource indication information sent by the network device, where the resource indication information is used to indicate a grant-free transmission resource that is allocated by the network device to the terminal device according to the information used to request the grant-free transmission resource; and determining, by the terminal device according to the resource indication information, the transmission resource used for performing grant-free transmission. According to the uplink data transmission method, the terminal device, and the network device in embodiments of the present invention, contention-based uplink data transmission can be implemented, and data transmission efficiency of a system can be improved.