A shell-and-tube heat exchanger and an air conditioning system. The shell-and-tube heat exchanger includes: a shell provided with a liquid inlet and an vapor outlet, the vapor outlet being disposed at an top portion of the shell; and a heat exchange tube bundle disposed in the shell in an axial direction of the shell; wherein the heat exchange tube bundle includes: a plurality of first heat exchange tubes located at an upper portion, the first heat exchange tubes having a first spacing therebetween; and a plurality of second heat exchange tubes located at a lower portion, the second heat exchange tubes having a second spacing therebetween; the first spacing is different from the second spacing.