The present study numerically and experimentally investigates the turbulent flow and heat transfer enhancement mechanisms of a serpentine air preheater, and further, the influence of geometrical parameters on thermal enhancement and flow resistance as well. The numerical simulation results coincided well with the experimental data. The results indicated that the structure with smaller path height ratios (HR = H/W) had promising enhancement capabilities, but larger pressure drop at the same time. Here, the factor HR is the ratio of height to width of the effective heat transfer flow path. The larger effective path length (L-e) had a positive effect on the thermal-hydraulic performance at lower Re number (Re<2,200), while smaller L-e displayed better performance on thermal enhancement at higher Re number (Re>2,200). With the nonlinear multiple regression methods, correlation for the averaged Nusselt number (Nu) was fitted by geometrical parameters L-e, HR and Re number.