This application provides a method for determining a time-domain resource used for grant-free transmission. The method includes: obtaining, by a terminal device, a first time-domain period and a second time-domain period of grant-free transmission resources, where a size of the first time-domain period is P1 time units, a size of the second time-domain period is P2 time units, and P1 is greater than or equal to P2; obtaining, by the terminal device, a quantity k of grant-free transmission resources in the first time-domain period; and determining, by the terminal device based on the first time-domain period, the second time-domain period, and the quantity k of grant-free transmission resources in the first time-domain period, an index of a time unit in which a grant-free transmission resource used for grant-free transmission is located. In this way, grant-free transmission resources configured for the terminal device in two adjacent periods do not overlap.