Abstract: This paper studies dissipation dynamics and final residues for chlorothalonil in cucumber and tomato cultivation in different seasons of Shandong Province, provide an evaluation for the safe use of chlorothalonil. The results show that the degradation of chlorothalonil could be described with equation：Ct=C0e-kt. In spring and autumn, the half life of chlorothalonil was 2.1d - 5.2d in cucumber and 3.1d - 6.0d in tomato, respectively. Chlorothalonil concentration applied at 2 - 3 times in cucumber and tomato with commanded dosage and 2 times commanded dosage, 7d after the last spraying，the residues of chlorothalonil was 3.101-0.912 mg?kg-1 in cucumber and 4.093～1.071 mg?kg-1 in tomato, respectively, The residues of chlorothalonil was less than 5.0 mg?kg-1 of maximum residue limit (MRL) of Codex Alimentarius Commission (CAC), Chlorothalonil degradation has seasonal variations, the commanded dosage of medication, cucumber and tomato safety interval should be about 7-10d in spring，and10-14d in autumn.