A shell-and-tube heat exchanger with externally-connected tube chambers includes a tube sheet, a shell, heat exchanging tubes, an inlet externally-connected tube chamber, and an outlet externally-connected tube chamber, wherein: the inlet and outlet externally-connected tube chambers are respectively fixed to corresponding positions of the tube sheet, two flow guiding devices are respectively located in the inlet and outlet externally-connected tube chambers, the two flow guiding devices respectively have two cavities therein, multiple flow guide channels outwardly extend from the cavities to the tube sheet and communicated with the tube sheet; one cavity of the outlet externally-connected tube chamber is communicated with a tube side outlet pipe, and one cavity of the inlet externally-connected tube chamber is communicated with a tube side inlet pipe. The shell-and-tube heat exchanger is reasonable in design, can effectively improve the sealing performance and reduce the tube side pressure drop, and has broad application prospects.