A beam configuration method, an apparatus, and a communication system. The method includes: a terminal device receives a beam configuration message, where the beam configuration message indicates a new beam. The terminal device may determine, at a time at which first duration starting from a first moment is reached, to use the new beam for communication. The first moment is a moment at which the terminal device switches to the new beam. In this case, the terminal device and the network node on which the old beam is located, and/or the terminal device and the network node on which the new beam is located can have consistent understandings on an effective time of the new beam, to achieve accurate communication.