Provided are a power adjustment method and apparatus for an unlicensed spectrum, and a terminal device and a network device. The method comprises: a terminal device adjusting, in a first transition period, a transmission power from turning-off to turning-on for a target transmission, wherein the first transition period and a first gap at least partially overlap in a time domain, the first gap comprises the length of time between an end moment of a first transmission and a start moment of the target transmission, and the first transmission is the most recent transmission before the target transmission.