The method includes: mapping, by a network device, a first PDCCH to A control channel transmission units on a first time-frequency resource, and mapping a second PDCCH to B control channel transmission units on a second time-frequency resource, where A is a positive integer and A≥2, B is a positive integer and B≥2, a subcarrier spacing of the first time-frequency resource is a first subcarrier spacing, a subcarrier spacing of the second time-frequency resource is a second subcarrier spacing, and the first subcarrier spacing is different from the second subcarrier spacing; and sending the first PDCCH and the second PDCCH.