Abstract: A comparative study on biomass and understorey species diversity during early stage (1~4a) of artificial vegetation (Melia toosendan) in the abandoned lands of Jinshajiang dry-hot valley of Heqing County was reported. The results showed that M. toosendan adapted itself to the environment of dry-hot valley well, grew and shaded well in the early stage. At the same time, it had a large biomass. However, it was very different in the dry weight of biomass of the individual and organs of 4-year old M. toosendan plantation between the south slope and the north slope in dry-hot valley. The biomass was higher on south slope than that on north slope. The biomass of individuals, trunks, branches, roots on south slope were (25.246±0.586), (14.986±0.203), (4.634±0.212), (5.626±0.223)kg respectively. Those on north slope were (16.580±0.206), (8.544±0.087), (2.895±0.067), (5.141±0.074)kg respectively. On the other hand, there were no obvious differences in moisture content of individuals and organs except for the roots in 4-year old M. toosendan plantation between the south slope and the north slope. The study of understorey species diversity showed that M. toosendan improved the growth environment of the abandoned lands, and increased its plant diversity and species richness.