The shell and tube heat exchanger is composed of a shell, a heat transfer tube bundle, a tube plate, a baffle plate, a baffle plate and a tube box. The shell is cylindrical, the inside is provided with a bundle, and the two ends of the tube bundle are fixed on the tube plate. Heat transfer of hot and cold two kinds of fluid, a flow in the tube, known as the tube side fluid; the other one in the tube flow, known as the shell side fluid. In order to improve the heat transfer coefficient of the tube, a plurality of baffles are arranged in the shell body. Baffle plate can improve the speed of the shell side fluid, forcing the fluid to pass through the tube, and enhance the degree of fluid turbulence. Heat exchanger on the tube plate in an equilateral triangle or square arrangement. An equilateral triangle arrangement is compact, tube outer fluid turbulence degree high, overall heat transfer coefficient; square array tube cleaning convenient for easy scaling of the fluid.