Abstract: Based on the character that varivance(v)is equal to mean(m)in Poisson distribution,a new aggregation index is presented in this paper,i.e La index(Lα=m-m/v +1).The index he can not only be used for testing insects population spatial pattern,but also represent the relationship between La and m,according to the property of Lα and m,the linear regression formula is presented,that is Lα-m model(Lα=θ+ηm).When the L-mis linear’the estimated parameter values of θ and η an offer different information con-cerning the spatial pattern of insect population. On the basis of the Lα-mmodel,a set of math formula for insects population sampling technique was derived.