Pinus sylvestris var. mongolica is one of important tree species, widely introduced into the arid and semi-arid zone in the northeast of China for shelterbelt establishment and timber production. However, in some places, this introduced pinus died with twigs and leaves wilted at first. In order to understand the cause of wilting and death, different plots were chosen to study the growth of the pinus associated with density, rainfall in Horqin Sandy Land of Inner Mongolia, China. The results showed that growth of the pinus related strongly to forest density. Death rate increased in power function with increasing of density. In the plot of the highest density, there were the least alive trees because of the highest death rate by now. The averaged death age, first death age, crown dimension, height and stem diameter decreased with increasing of density. The height still related to density in arid zone, though size-density theory showed that height growth was relatively unaffected by competition. Twig wilting was mainly attributed to high density. In plots of low density, proportion of twig-wilted trees was lower and there was nearly no obvious influence on growth of trees. There was not significant difference of crown dimension to stem diameter in the plots, and averaged value was only 0.297. Thus, according to Dawkins’ report, we think that this region may be more suitable for monoculture than mixed forest. Anyway, climate and soil condition in this region are suitable for planting the pinus. The original density should be controlled under 2800 trees/hm^２. At the same time, intermediate cutting should be taken into account when growing-peak is coming. It is reasonable that the density is about 2100 per hectare when tree age is 20 years old approximately.