Abstract: In order to explore the possible reasons of the excessive pesticide residues in celery and reduce the over standard rate of pesticide residue, the author investigated the residue and degradation dynamics of chlorpyrifos in celery in winter greenhouse and open field by 2 years’ degradation dynamic tests, and conducted the control test on Chinese cabbage under the same condition. The results showed that the residue half-life of chlorpyrifos in greenhouse celery was 11-12 d under different doses, while it was 4-6 d in Chinese cabbage, which indicated that the degradation rate of chlorpyrifos in greenhouse celery was significantly lower than that of Chinese cabbage. The half-life of chlorpyrifos in open field celery was 9-10 d, which was faster than that in greenhouse celery. Therefore, the author suggested that the safety interval period of chlorpyrifos in celery should be 60 d, and the control of chlorpyrifos treatment should be strengthened or using the degradable biological pesticides in the process of celery production.