Abstract: Edge error of simulation system based on individual tree model and its negative effect on stand growth prediction were discussed in this paper.It is proposed that guard lane,which is established to prevent object trees from the disturbance of edge error,should consist of two independent parts,i.e,edge influence band which should be two times the width of a tree influence radius and error resistance one which could be estimated through age class numbers and allowable prediction error.The influence of edge error is dying away as propagating from the boundary to centre of a plot.Systematic error of trees' competition index could be assessed according to their position in a stand,so systematic error of tree growth prediction could be evaluated with the help of a transitive operator,which is used to transfer the relative error of competition index into the relative one of growth prediction and is deduced from a generalized tree growth function.The result presented here can be used to decide with what width of guard lane the sound result might be worked out through the individual tree based model.