A terminal access method is disclosed. The method includes the following steps: the terminal receives an auxiliary synchronization signal sent by a base station on a transmission resource which is chosen from an uplink and used for transmitting downlink data; the terminal calculates transmission power according to the auxiliary synchronization signal; and the terminal sends a Random Access Channel (RACH) access preamble code to the base station according to the transmission power and performs a RACH access process. In this technical solution, the auxiliary synchronization signal is transmitted in a special sub-frame selected from the uplink, which makes it possible for the terminal to obtain the channel quality information of the uplink by receiving the auxiliary synchronization signal during a cell synchronization stage, and determine the transmission power according to the channel quality information of the uplink before the RACH process occurs, thereby reducing the step of adjusting the transmission power and shortening the time of the random access of the channel. A terminal access system and associated devices are also provided.