Abstract: P.'popularis' is the hybrids,Selected from P.simoii fertilized by the pollen mixture of P.nigra var.italica and Salix matsudana (1:8).In order to know if the second male has function in the process,The author has analysied the genetic mechanism of P.popularis with immunochemical technique. The double immunodiffusion was made between serum of anti-Salix total proteins with proteins from 9 'popularis' clones,and controlled samples,with 5 clones of the hybrid of P.opera (P.simonii×P.nigra var.italica).The comparison of the resulted immunoprecipitation lines showed: (1) The number of immunoprecipitation lines of'Popularis' is more than that of the hybrid of P.opera (2) Beyond the other clones.'Popularis' 39 and 40 presented an extra peculiar immunoprecipitation line, (3) The precipitation line of 'Popularis' is stronger than that of hybrid of P.opera It is likely,therefore,that DNA fragments of salix were assimilated and integrated into the zygote of P.simonii×P.opera. According to this experiment and many other evidences we believe that the fertilizing with double males is feasible method for breeder who want to get a hybrid which integrated the second male's DNA fragments,and maybe it is more suitable for the.plants which can be cloned easily.