An investigation was made on the ratio of infested peach trees and the population density of the longicorn larvae in 1– to 20–year–old peach orchards, which is located in Jingzhou County, Hunan Province, a semi–closed ecosystem to compare the differences of spatial distribution patterns of Aromia bungii (A. bungii) larvae in peach orchards with different tree ages by using five aggregation indexes examination and two regressions analysis. The results indicated that the 1– to 2–year–old trees were not infested by A. bungii larvae which attacks peach tree at and above 3–year–old. The ratio of infested trees and the average population density of longicorn larvae significant increased with increasing tree ages, in 19– to 20–year–old peach orchards, the ratio of infested trees was above 90% and the average population density was above 2 beetles per tree. The larvae of A. bungii had an aggregated spatial pattern and showed density dependence, in which aggreation increased with increasing population density. In 3– to 15–year–old peach orchards, A. bungii larvae exhibited aggregated distribution basically composed of individual group in which larvae attracted mutually among individuals. In 16– to 17–year–old peach orchards, A. bungii larvae showed random distribution or uniform distribution while in 19– to 20–years–old, showed aggregated distribution in which the basic component was individuals which repelled one another. Using the spatial distribution information of A. bungii larvae, the sampling formula for A. bungii larvae populations in peach orchards with different tree ages was established. According to the theoretical sampling formula, the smaller the density of A. bungii larvae, the larger the sampleing quantity, andwhereas the smaller the sampleing quantity is low when the density is high. Based on sequential sampling formula, the sampling quantity of A. bungii larvae in 3– to 20–year–old peach orchards were divided into six sections: peach orchards of 3 to 4 years old, of 5 to 6 years old, of 7 to 8 years old, of 9 to 13 and 19 to 20 years old, of 14 to 15 years old and of 16 to 18 years old.