Disclosed in the present application are a method and device for feeding back downlink data. When a processing duration of an UE is shortened, feedback timing information for feeding back downlink data may be adaptively changed. The method comprises: determining a processing capability of an UE, the processing capability referring to a processing duration that the UE takes to process the received downlink data to determine whether said downlink data needs to be retransmitted; according to the determined processing capability, determining the feedback timing information of the UE feeding back the downlink data.