The invention discloses a shell and tube heat exchanger with novel baffle plates. The shell and tube heat exchanger comprises a tube pass inlet, a tube pass outlet, a left seal head, a right seal head, a shell pass inlet, a shell pass outlet, a shell, a tube plate, tube holes, the circular baffle plate, the regular hexagon baffle plate, heat exchange tubes, semicircular small holes and a circular ring. The two baffle plates are alternately arranged in the shell. The middle of the circular baffle plate is provided with the circular ring with the diameter being 5-6 times of the outer diameter of the heat exchange tubes for passing of shell pass media. The three semicircular small holes spaced by 120 degrees are formed in an edge tube hole of the circular baffle plate, the three semicircular small holes spaced by 120 degrees are formed in a middle tube hole of the regular hexagon baffle plate, and a small part of shell pass media can flow through the semicircular small holes. According to the heat exchanger, the heat exchange performance can be improved, and meanwhile deposition of dirt on the heat exchange tube walls is effectively reduced.