Abstract: Spatial distribution patterns for egg-masses,small larvae,large larvae and cocoons of the pine caterpillar were measured by means of several indexes of aggregation in Zhe Jiang Province.Frequency distribution of eggmasses fits to Poisson distribution quite well,and that of the small larvae, large larvae and cocoons obeys aggregation distribution,but the aggregation indexes are highest in small larvae and lowest in cocoons. Iwao's method of regression of mean crowding()on mean density() is a good method for detecting the aggregation patterns.In the pine caterpillar, small larvae,large larvae and cocoons,all relation in a series of distribution is fitted to a single linear regression for α>0,β>1.Iwao's equations for data transformation were applied and tested for its fitness,the transformed data all obey normal distribution and the tests of heterogeneity of variance and non-additivity indicate that the results of transformation are well fitted. From this method the optimal sampling size is determined,the sequential analysis is also applied. In the pine caterpillar,the basic component of the distribution (i.e.large larvae) is a loose colony.The size of the colony and the distribution of individuals in colony remain to be studied.