Embodiments of the present invention disclose a method for awaking an optical network unit in a passive optical network, including: receiving, by an optical line terminal OLT, a service packet corresponding to an ONU in an energy-saving mode, where the service packet carries a packet feature, and the packet feature indicates a service type of the service packet; detecting, by the OLT, the packet feature of the service packet; and when the packet feature of the service packet is a preset packet feature of needing to awake the ONU, awaking, by the OLT, the ONU in the energy-saving mode. According to the technical solutions provided in the embodiments of the present invention, an ONU can be awoken from an energy-saving mode in time when a traffic rate at an initial service stage is small, and a high QoS requirement of a service is met.