A channel assessment method, a channel assessment apparatus, a terminal and a base station when a LTE system operates in an unlicensed band are provided, where the method includes: receiving an uplink scheduling instruction transmitted in a subframe n by a base station, where the uplink scheduling instruction is configured to instruct a terminal to transmit uplink data in a subframe n+i by using an allocated resource; and setting channel assessment time in a subframe after the subframe n and before the subframe n+i, so as to detect a clear or busy state of an uplink channel to be occupied by the terminal.