A power headroom transmission method and a device are provided. The transmission method is applied to a terminal device that supports use of two different types of waveform for data transmission, the terminal sends a first power headroom information and ΔM, wherein the first power headroom information is used to indicate power headroom of the terminal device when data is transmitted by using the first waveform, ΔM is a difference between a first maximum power and a second maximum power of the terminal device, the first maximum is a maximum power when using the first waveform, the second maximum is a maximum power when using the second waveform.