A heat exchanger (100) and an air-conditioning system. The heat exchanger (100) comprises: a group of first heat exchange tubes (T1) for forming a first loop (C1); a group of second heat exchange tubes (T2) for forming a second loop (C2); and a group of fins (3), at least a plurality of fins (3) in the group of fins (3) being in contact with both at least a plurality of first heat exchange tubes (1) in the group of first heat exchange tubes (T1), and at least a plurality of second heat exchange tubes (T2) in the group of second heat exchange tubes (T2). If one loop of an air-conditioning system having two loops is closed, heat exchange regions of the fins for the loop can be used in the other loop, thereby improving the heat exchange efficiency of a heat exchanger.