The disclosure provides an uplink transmission method, a terminal, and a network side device. The method includes: pre-allocating, by a network side device, an uplink transmission time-frequency resource to a terminal, and storing, by the terminal, the uplink transmission resource; and when the terminal needs to send a data packet, sending, by the terminal, the data packet to the network side device by using the uplink transmission resource, where the data packet includes indication information, the indication information is used to indicate whether the data packet is initially transmitted by the terminal or the data packet is retransmitted by the terminal, and the network side device can correctly receive the data packet and perform combination processing on the data packet based on the indication information. According to embodiments of the disclosure, reliability of grant-free transmission can be ensured, and communication performance can be effectively improved.