Embodiments of the present invention relate to a data transmission method, an access point, a relay node, and a data node for packet aggregation. The data transmission method for packet aggregation includes: determining an aggregation relay node in a service area, for aggregating a Medium Access Control (MAC) frame that is sent by a data node to an access point (AP) and is forwarded by the aggregation relay node; and receiving an aggregated MAC frame sent by the aggregation relay node, where the aggregated MAC frame is a MAC frame that is sent by the data node and is aggregated by the aggregation relay node. According to the embodiments of the present invention, a relay node is selectively used to aggregate data, so that aggregated packet data quickly reaches a scale for transmission, and the packet data is sent to a destination node within a short time, thereby significantly enhancing quality of service of a delay-sensitive application service.