Abstract: Crossing tetraploid with diploid is the most effective approach for triploid production in plants. In order to increase the efficiency of tetraploid induction, techniques of inducing tetraploids through zygotic chromosome doubling of Populus were studied preliminarily, treating female catkins of P.pseudo-simonii× P. nigra ‘Zheyin 3#’ 6－9 days after pollination with 0.5% colchicine solution and 38－44℃ high temperature, and 8 tetraploids were produced. In these tetraploids, three were produced by immersing catkins of P. pseudo-simonii × P. nigra ‘Zheyin 3#’ 7 days after pollination with 0.5% colchicine solution for 24 h; five were obtained by treating the catkins 7－8 days after pollination with 38, 41 and 44℃ high temperature for 4 h. According to the results, it is inferred that the first mitosis of zygotes of the ‘Zheyin 3#’ is probable to take place 7－8 days after pollination, which is fit to enforce treatments to induce tetraploids.