The present invention provides a method for transmitting downlink control information, a network side device, and a user equipment. The method includes: selecting, by a network side device, a aggregation level of a physical control channel set in a transmission subframe, and selecting the number of physical control channel candidates corresponding to the aggregation level according to the aggregation level; and sending, by the network side, downlink control information on a physical control channel candidate corresponding to the selected number. The times that blind detection is performed corresponding to the aggregation level corresponds to the number of physical control channel candidates, and therefore, when the number of physical control channel candidates is determined, the times that blind detection is performed is determined, so that the network side device and the user equipment can communicate with each other without increasing the times that blind detection is performed.