A combined serial two shell-pass shell-and-tube heat exchanger (CSTSP-STHX) with continuous helical baffles has been proposed to improve heat transfer performance. This CSTSP-STHX separates the shell side into two individual shell passes. The inner shell pass is conventional segmental baffled, and the outer shell pass is continuous helical baffled. The working fluid flows through the outer and inner shell passes in sequence. The thermo hydraulic performances of CSTSP-STHX are experimentally compared with the double shell-pass shell-and-tube heat exchanger with segmental baffles (SG-STHX). The results show that the CSTSP-STHX gets greater shell-side heat transfer coefficient and pressure drop, furthermore it also has better heat transfer coefficient under the same pressure drop than those of the SG-STHX. Finally it should be emphasized that the leakage on annulus separator has to be as possible as reduced. The present studies are beneficial for the design and practical operation of CSTSP-STHX. (C) 2016 Elsevier Ltd. All rights reserved.