The present invention discloses a method for detecting downlink control information, including: when scheduling across carriers is enabled, determining by user equipment (UE) user-specific search space monitoring a physical downlink control channel (PDCCH) according to component carrier indexes, wherein the component carrier indexes include component carrier indexes corresponding to various component carriers implementing scheduling across carrier and being scheduled across carriers. Also the present invention also provides an apparatus for detecting downlink control information, a user equipment and a network side device. The present invention solve the overlap problem of common search space and user-specific search space in Release 10 and solves the problem of determining a search space for the PDCCH in the situation of scheduling across carriers is enabled in Release 10.