This application provides a parameter determining method, a monitoring method, and a communications apparatus. The method includes: configuring, by a network device, a plurality of serving cells for a terminal, where at least two of the plurality of serving cells have different subcarrier spacings; and determining, by the network device based on at least one of subcarrier spacings of the plurality of serving cells, a maximum number of physical downlink control channel PDCCH candidates monitored by the terminal in a unit time. According to this application, a maximum number of PDCCH candidates monitored by a terminal in one time unit can be determined when carriers for carrier aggregation correspond to different subcarrier spacings.