Abstract: In order to determine the spatial distribution pattern of tobacco potato virus Y,the aggregation indexes of the data from 11 field disease investigations were calculated,the clumping index(I),Cassie index(CA),patch index(m^*/m) and dispersion coefficient(C) at different incidences were analyzed,and the theoretical sampling numbers at different incidences were also calculated with I wao's formula.The results indicated that the field diseased plants assumed an aggregated distribution pattern,the diseased indivi-duals attracted each other and the basic distribution component was group of individuals when the diseased plant density was below 4.32653 plants/25 plants(disease incidence <17.31%);the diseased plants assumed an uniform distribution pattern when their density reached 5.48148 to 7.96296 plants/25 plants(disease incidence was 21.93% to 31.85%).The theoretical sampling number for aggregated distribution should be larger than that for uniform distribution.The sample number would be 2950 to 425 plants when the disease incidence was in the range of 1.143% to 9.061%.