A transmission method includes: a terminal device receives an uplink grant from a base station; and the terminal device sends a report to the base station, where the report includes a power headroom of each of at least one uplink subcarrier, and/or a power headroom of each of at least one bandwidth part. According to the uplink data transmission method, the terminal device, and the base station in embodiments of this disclosure, a power headroom can be reported at a finer granularity.