Embodiments of the present application provide a method for monitoring a PDCCH, a terminal device, and a network device, capable of reducing power consumption when a terminal device monitors a PDCCH. The method comprises: a terminal device receiving a first message sent by a network device, the first message indicating a first time duration and/or whether to monitor a PDCCH within the first time duration; and the terminal device monitoring the PDCCH according to the first message.