Embodiments of the present application provide a method and apparatus for determining a measurement gap, and a terminal device. The method comprises: a terminal device determines that a switch from a source BWP to a target BWP is triggered, the source BWP switching to being associated with a first measurement gap configuration, and the target BWP being associated with a second measurement gap configuration; and the terminal determines, in the first measurement gap configuration and the second measurement gap configuration, a measurement gap configuration to be activated or enabled, and uses the activated or enabled measurement gap configuration to execute a measurement.