Abstract: The accuracy of site index curves has been estimated by using the 24-term time series h₍₃₀₎(i, t_j)=β₁(t_j)h₍₃₀₎(i, t_(j-1))+β₂(t_j)h₍₃₀₎(i, t_(j-2)+β₃(t_j)h(30)(i, t_(j-3))+ε(i, t_j)which is simulated by tetrachoric model in 4 site types of larch (Larix olgensis Henry)plantation. The test result showed that the degree of accuracy of site index curve fitted by data of temporary plots is the highest and the mean square error varies within 0.2-7.3dm.