Taking the root-tip of Tagetes erecta L.‘QU2-2’ as the experimental material，the material taking time，length of the root，material pretreatment method，dissociating time，dyeing time and squashing tools were screened and optimized.The results showed that using indoor root culture，observed the high-quality images of the chromosomes of root-tips at 9:14，1.0 cm of the root length，the cool water pretreatment (0～4℃)，1.0 mol/L HCl for dissociation in 7 minutes，dyeing in 25 minutes，squashing the slides with a rubber head pencil，could observe clear mitotic prometaphase.