Abstract: To study the effect of herbicides on weeding, and safety and yield of tartary buckwheat in autumn sowing field in Yunnan,‘Yunqiao 1’was used as material, four treatments were conducted: no weeding, artificial weeding , chemical weeding (S-metolachlor and acetochlor) and spray on soil before seedling. The results showed that S- metolachlor and acetochlor had good control effect on weeds in autumn tartary buckwheat field, and the effect of S-metolachlor on broad leaf grass was higher than that on grassy weed; the control effect of acetochlor on grassy weed was higher than that on broad leaf grass. However, both of them inhibited the emergence and growth of tartary buckwheat seedling, and seriously affected the yield of buckwheat. Therefore, we recommend that S-metolachlor should be used for buckwheat fields dominated by broad leaf grass, and acetochlor herbicide should be used for tartary buckwheat fields dominated by grassy weed. We need further to detect and screen out the optimum concentration of herbicide for tartary buckwheat field, which has better control effect and does not affect the yield.