Abstract: On the basis of the character that varivance(V) is equal to mean (m) in Poisson distribution,a new aggregation index is presented in this paper,I.e L index (L =V/m+V).The index L can be used for testing insects population spatial pattern;and also the relationship between L and V is usually linear,according to the property of L and V,the linear regression formula is presented by author,that is L -V model (L =a+Bv).When the L -V is linear,the estimated parameters values of a and b can offer different information concerning the spatial pattern of insect population.On the basis of the L -V model,the author developed a set of math formula for insects population sampling technique.