[Objective] The hydrological regulation by aboveground vegetation layer of two forest types, including secondary poplar-birch forest(13 a, 18 a, 28 a) and larch plantation(9 a, 13 a, 15 a, 20 a) in the northern mountainous region of Hebei Province, was compared in order to provide a support for evaluating how forests conversion influences the hydrological process in the region.[Methods] The litter stock, biomass of different forests and their water interceptions were measured by stardard sample and testing mothods.[Results] (1) Water interceptions of aboveground layers of larch plantations were significantly greater than those of secondary poplar-birch forests.(2) Layers of the two forests had different water interception abilities with a rank as:litter >canopy >shrub layer.(3) The canopy interceptions of the larch plantations with young and middle age were better than that of the secondary poplar-birch forests with the same ages, but the near-mature secondary poplar-birch forest performed better than the larch plantation because of the decreased stand density by thinning.(4) Litter water interceptions of larch plantations with different ages were greater than that of secondary poplar-birch forests, e.g. the litter water interceptions of 13 years larch plantation and secondary poplar-birch forests were 35.36±6.50 t/hm² and 15.79±4.85 t/hm², respectively.[Conclusion] It was concluded that the aboveground layer of larch plantations had remarkable hydrological regulation function, and sometime it was higher than that of the secondary poplar-birch forest in the northern mountainous region of Hebei Province. Forest thinning can lead to the decrease of hydrological regulation of aboveground vegetation layer to some extent.