Abstract: The percentages of Ⅰ-Ⅲ instars and Ⅳ instar+wingless agamic females of tobacco aphid,Myzus nicotianae (Blackman),on flue-cured tobacco K-326 between different leaf phyllotaxy were quite different.The difference obviously depended on the aphid density.The caculation of seven spatial pattern indices indicated that the vertical spatial distributions of the Ⅰ-Ⅲ instars and Ⅳ instar+wingless agamic females on tobacco were contagious distribution at every density.The mean value of the spatial pattern indices showed the aggregating intensity of Ⅰ-Ⅲ instars was stronger than that of the Ⅳ instar+wingless agamic females.The vertical spatial distribution of Ⅰ-Ⅲ instars,Ⅳ instar+wingless agamic females and whole wingless aphids were analyzed by ways of three regression models.It demonstrated that the distributions of the tobacco aphids at any density were contagious,and the aggregating degree was density-dependent.The basic component in the distribution was the individual groups and the population density had little influence on the relative aggregating degree of the basic component in the distribution.