Abstract: Pinus yunnanensis forests were invaded and disturbed by Eupatorium adenophorum,and P.yunnanensis seedlings were difficult to regenerate under the forests.Soil seed bank characteristics and population structure of P.yunnanensis forest invaded by E.adenophorum in Humashan,Kunming,Yunnan Provine,were studied to find out the reasons for bad natural regeneration and the decline of the populations.The results showed that the seeds storage in 0—2cm,litter layer,2—5cm,5—10cm were 2723.4,1567.2,1365.6,1107.8seeds/m2,accounting for 40.26%,23.17%,20.19%,16.38% of total storage,respectively.There were 52 seed spieces,which belong to 25 families and 49 genera.Composite was the dominant family,with a density of 5475.0seeds/m2,accounting for 80.94% of total storage.Eupatorium was the dominant genus,and E.adenophorum was the dominant species,both with a density of 5262.5seeds/m2,accounting for 77.80% of total storage.Herb speices were the dominant life form which has 41 speices,the density of the herb species seeds was 6504.7seeds/m2,accounting for 96.17% of total storage in the soil seeds bank.There were 9 shrub species with a density of 256.3seeds/m2,accounting for 3.79% of total storage.There were only 2 tree species with a density of 3.1 seeds/m2,accounting for 0.05% of total storage.Population of P.yunnanensisis was a declined population with which its age structure was similar to inverted pyramid shape.The seed storage of seed bank of E.adenophorum and P.yunnanensis was 5262.5seeds/m2,1.6seeds/m2,respectively,with a ratio of 3368∶1.The reserve of survival seeds of P.yunnanensis in the forest was very few,which was one reason of bad natural regeneration and population decline;whereas the abundant seeds reserve of E.adenophorum,could be one of the potential barrier in the natural regeneration of P.yunnanensis.