This study analyzed five varieties of P. tomentosa and their putative parents, P. alba, P. davidiana, P. adenopoda and P. tremula by RAPD and artificial cross. Of 78 bands revealed by 13 arbitrary primers selected, 58 (74.36%) bands were polymorphic among P. tomentosa and four putative parents. The RAPD statistical results showed the relationship between P. tomentosa and P. alba or P. adenopoda was closer than that between P. tomentosa and P. davidiana or P. tremula . There were higher similarity and lower genetic distance between P. tomentosa and P. alba or P. adenopoda than that between P. tomentosa and the other two putative parents. The results from UPGMA, Fitch margoliash phylogenetic dendrogram were similar. In addition, artificial hybrids including  reciprocal cross between P. alba and P. adenopoda were used to compare with five varieties of P. tomentosa . And those hybrids between P. alba as female and P. adenopoda as  male were closer to P. tomentosa than those from reciprocal cross. The results demonstrated that P. tomentosa was a natural hybrid between P. alba as female parent and P. adenopoda as male parent.