Abstract: One problem which should be solved is how to determine window width when theories and methods of nonparametric kernel density are employed to simulate stand structures,which is also the core of applying the nonparametric kernel density estimation in practice and directly related to simulation precision.Five methods of determining window width were provided in this paper,i.e.,minimum integral mean square of errors,maximum likelihood,chi-square test,normal distribution,and empirical equation,which basically met the requirements in forestry.One example was given out to obtain optimum window width by means of chi-square test method with 13 natural forest plots sampled from Wangqing forestry bureau,Jilin Province.