The circumferential overlap structure is considered as one of the key factors which influence the performances of helical baffle heat exchangers by restraining the bypass stream between adjacent baffles. The flow and thermal performances of four trisection helical baffle heat exchangers with the same angle of inclination but different circumferential overlap sizes were numerically investigated. The four schemes involve an end-to-end one and three circumferential overlap ones with triangular area covering one row (20 degrees TCO), two rows (20 degrees T2CO), and three rows (20 degrees T3CO) of tubes. The flow field and combined slices with pressure contours plus velocity vectors were depicted. The 20 degrees TCO scheme proved to be superior to other schemes since its Nusselt number as well as its comprehensive index are the highest and its secondary flow is the strongest.