Abstract:To understand the impact of forest structure on the evapotranspiration (ET) and its components, three coniferous forests including Pinus armandii natural forest, Pinus tabulaeformis plantation and larch(Larix principis-rupprechtii)plantation were selected to estimate the ET, forest transpiration(Tf), the sum of soil evaporation and herbage evapotranspiration(ETsg), canopy interception(I), shrub transpiration(Ts) from May to October 2012 by using thermal dissipation technique and hydrological methodology in a small catchment named Xiangshuihe of Liupan Mountains. The results indicated that, the ET of P. armandii forest, P. tablaeformis forest and larch forest were 413.2, 377.6, 568.2 mm, respectively accounted for 81.5, 74.4 and 115.1 % of the rainfall at the same period, but it’s components are different. The allocation of ET in the vertical layers performed similarly among the three forests, but the ratio of each component to total ET significantly differed. The I of P. armandii forest, P. tablaeformis forest and larch forest were 146.8, 115.1, 177.2 mm, respectively accounted for 35.53%, 30.48% and 31.19% of the ET, and this was a result of a higher leaf area index (5.16) in natural forest stand than that of larch plantation (4.78 ) and P. tablaeformis plantation(3.66). Affected by the forest density, the Tf (mm) was range as follows: larch(209.8)>P. tablaeformis (152.8)>P. armandii (88.3). The Ts differed notably among three forest, with the maximal value (106.9mm) in natural forest, followed by the larch(26.8mm) plantation, and the minimal value (24.7mm) of the P. tablaeformis plantation, this was because of lower shrub coverage in the plantation. The ETsg of larch and P. tablaeformis plantation was 154.4 and 102.3 mm, respectively, which was 2.17 and 1.1.44 times higher than natural forest, and this might be contributed to more solar radiation received in the herb and soil layer in the plantation than natural forest. The forest structure was an important factor that causes the evapotranspiration of artificial forest to be higher than that of natural forest, and the selection of reasonable tree species and forest substructure was the key to keep the regional water resources safe.