Embodiments of the present invention disclose a method, an apparatus, and a system for transmitting data and relate to the communications field. In order to enable more flexible configuration of flexible subframes and increase downlink throughput, a technical solution provided in the present invention is as follows: configuring an HARQ synchronization attribute of a data packet, where the HARQ synchronization attribute includes synchronous HARQ or asynchronous HARQ; configuring an HARQ process ID of the data packet when the HARQ synchronization attribute is configured to asynchronous HARQ; and sending downlink control information for scheduling the data packet to a user equipment.