Abstract: Based on the density theory of plant growth and related biological hypothesis,a new model of self-thinning law of plant population was proposed,i.e. N =exp( aln² B+bln B+c ),where N and B is population density and weight mean plant or mean basal area at DBH and a,b and c are parameters.It was proved that the model fitted observed data very well from Pinus tabulaeformis population,and which was very simple.Therefor,the model is a satisfactory expression of self-thinning law of plant po pulation.