A service implementation method, apparatus, and system are disclosed. The service implementation method includes: receiving, by a serving gateway, a data packet of a terminal device sent by a packet data network gateway; if the data packet is a data packet with a serving priority and the serving gateway has sent a paging trigger message with a serving priority to a mobility management element, skipping, by the serving gateway, sending a paging trigger message to the mobility management element; or if the data packet is a data packet with a serving priority and the serving gateway has sent no paging trigger message with a serving priority to a mobility management element, sending, by the serving gateway, a paging trigger message to the mobility management element; wherein the paging trigger message is used to enable the mobility management element to page the terminal device.