Abstract: In order to explore the optimal conditions of polyploidy induction, Platycladus orientalis’s root tips are applied to colchicine and four major factors including colchicine concentration, temperature, handling modes and light condition are adopted in orthogonal design. The result shows that the rate of polyploidy induction can reach at 92.7% under the condition of 25℃, darkness, 72 hours later and soaked in 0.3% concentration of colchicine solution directly, which provides a base on future studies in polyploidy breeding of Platycladus orientalis.