Abstract: M=a₁H_t^b₁c₁ and M=a₂D^b₂N^c₂. are regarded as the binary mathematical models for the equiheight line and equidiameter line respectively, and M = a₃D^b₂H^c₂N^d₂ as the cubic mathematical model for the complex equiheight-equidiameter line, which can fully reflect the relation among stand density and amount of volume and its changing rule precisely. It is proved that the bases and method for drawing up the models are significant widely.

Key words: Equiheight line, Equidiameter line, Methematical model, The maximum density line, Plots in order