An uplink service data transmission method and apparatus. The method includes: receiving, by a wireless local area network WLAN access point AP, first indication information sent by a cellular network access device, where the first indication information is used to instruct the WLAN AP that user equipment UE served by the cellular network access device has uplink service data on which service offloading needs to be performed to the WLAN AP; and sending, by the WLAN AP, second indication information to the UE according to the first indication information, where the second indication information is used to instruct the UE to send the uplink service data to the WLAN AP.