Abstract: In order to explore the reason why residue of pesticides in celery easily exceeds their MRLs,the study of chlorpyrifos was carried out to decide its adhesive rate on surface of celery and pakchoi (a variety of Chinese cabbage) and absorbing and transmitting ability on leaf and root.The results showed that the adhesive rate on celery dipping in 857 mg/L chlorpyrifos is significantly higher than that of pakchoi,being 41.5% and 26.4% respectively.When chlorpyrifos solution added with 240 mg/L polyalkyleneoxide modified heptamethyltri siloxane,PHM (organo-silicon surfactant) ,the adhesive rate observably increased by 7.2% for celery,while the value is insignificantly affected for pakchoi.Chlorpyrifos was easily absorbed when it was daubed on the leaf and irrigated the root,4.99 and 4.23 mg/kg were found respectively in the untreated parts 0.5 day after daubed with 950 mg/L chlorpyrifos solution.The residue concentrations of the above half parts of celery and pakchoi were 0.96 and 0.22 mg/kg 2 days after root irrigation with 480 mg/L chlorpyrifos solution.The results showed that the adhesive and absorbing ability of chlorpyrifos in cerley is higher than that in pakchoi.Cerely should not be classified into the same species with pakchoi but with other similar vegetables so that pesticides application rate and frequency,residue regulation,pre-harvest interval (PHI) and MRLs for the same kind vegetable are also fit for celery.