Abstract: Coffee stem-borers 〔Acalolepta cervinus (Hope) and Xylotrechuse quadripes Chevr.〕are two major pests damaging coffee trees in Yunnan Province.This study shows that the spatial distribution of mixed population is of random distribution based on Taylors model,Poissons index and Morisitas index.Additionally,the empirical models for estimating the density and determining the sample size are developed in this study.These models might be of practical value.