The study showed that there was a power function relationship between weight per tiller and density of two ecotype Leymus chinensis populations in Songnen Plain, and the b value in the function (-0.098 approximately -0.272) was bigger than -1. The biomass and weight per tiller of the two populations increased with their increasing density and height, and the relationships between biomass and density, and between weight per tiller and height were significantly accorded with power or liner function. In the period of vegetation growth, the biomass and weight per tiller of the two populations had the smallest change speed, and the b value of grey-green ecotype (0.7872 and 0.0134) was smaller than that of yellow-green ecotype (0.8793 and 0.0222). On the contrary, in the period of post-fruiting vegetation growth, the b value of grey-green ecotype (0.8048 and 0.0303) became bigger than that of yellow-green ecotype (0.7796 and 0.0258). It was suggested that the two ecotype L. chinensis populations did not reach environment capacity in the sampling field. They kept on growing during the whole growth period, with the same growth pattern, and grey-green ecotype had a stronger potential capability of growing.