In the spatial pattem of the eggs of diamondback moth,Plutella xylostella(L.)there was sometimes obvious edge-effect.Based on the relationship between the eggsdensity(De)and the shortest distance(h)of sample point to the border of thearea of the host plant distribution,a new model was developped:De=a+be-ch,whichcould well describe the spatial pattem with edge-effect.In above model,threeparameters all have explicit biological meanings,a,b,and c denote the density whenedge-effect was not exist,the addition of the density when edge-effect reached themaximum,and the coefficient of the decline of edge-effect respectively. Accordingto these parameters,two indices were gained.One was strength of edge-effect(s)(s=b/a),which could be used to analyse the mechanism for the formation of spatialpattern.Another was width of edge-effect stratum(w)(w=ln(10s)/c,which couldserve as a basis for stratified sampling.The procedure of stratification and theoreticalnumber of samples for stratified sampling were also discussed.