Disclosed in the present invention are a heat exchanger and an air conditioning system having same. The heat exchanger comprises: a first heat exchanger core comprising a first sub-heat exchanger core and a second sub-heat exchanger core, wherein the first sub-heat exchanger core and the second sub-heat exchanger core comprise heat exchange tubes, the heat exchange tubes of the first sub-heat exchanger core and the second sub-heat exchanger core are connected to each other, and orthographic projections of the first sub-heat exchanger core and the second sub-heat exchanger core on a plane where the second sub-heat exchanger core is located at least overlap partially; and a second heat exchanger core comprising a heat exchange tube, wherein the heat exchange tube of the second heat exchanger core is connected to the heat exchange tubes of the first sub-heat exchanger core and the second sub-heat exchanger core. At the same incoming wind speed, the ratio of the wind resistance of the heat exchanger to the air passing through the first heat exchanger core to the wind resistance of the heat exchanger to the air passing through the second heat exchanger core is less than a predetermined value. By using the heat exchanger according to the present invention, the performance of the heat exchanger can be improved.