Abstract In this study, we have examined local flame structure by joint PLIF imaging, using simultaneous HCHO/OH-PLIF and orthogonal OH-PLIF measurements. By considering the degree of flame wrinkling, three-dimensional flame surface area is obtained from 2D images. We have used a cyclone–jet combustor to establish turbulent premixed flames for propane/air mixtures in a wide range of turbulence, covering the flamelet regime and thin-reaction-zones regime on combustion diagram. Results show that as the mean velocity at the combustor exit is increased, more complex flame structure is observed with multiple flamelets. Near the global extinction, peak OH concentration in reaction zone becomes almost zero whereas HCHO concentration in preheat zone still remains. As a result, the large reduction of heat release rate occurs, resulting in local extinction. The turbulent burning velocity determined by the mean flame shape is increased with turbulence, and the bending effect is observed in thin-reaction-zones regime. On the other hand, different from the flame perimeter, the flame surface area is linearly increased. Since the turbulent burning velocity is well predicted by the classical formula in wrinkled flames, the bending is explained by the reduction of local burning velocity. Thus, within the frame work in our measurement, the flamelet approach could be still valid even in the thin-reaction-zones regime.