Abstract:M=a1Htb1c1 and M=a2Db2Nc2. are regarded as the binary mathematical models for the equiheight line and equidiameter line respectively, and M = a3Db2Hc2Nd2 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.