Abstract: To determine the changes in residue and environmental safety of chlorpyrifos application on pakchoi under greenhouse conditions, the residue dynamics and final residues of chlorpyrifos in pakchoi was studied by the methods of gas chromatography and field experiment. Meanwhile, a safe application method of the insecticide was explored to provide a guideline for application of chlorpyrifos in field, and to refine and update the residue data while helping to determine the harvest interval. The results showed that the dynamics of chlorpyrifos residue in pakchoi followed first-order kinetic equation, and the half\|life of chlorpyrifos was 1.161-1.438 days. A positive correlation was found between pesticide residue in pakchoi and field dosage of pesticide, the digestion rate of pesticide residue in pakchoi slowed down and the residual quantity increased with the raising pesticide application concentration. With one application of the recommended concentration for chlorpyrifos, the safety interval of chlorpyrifos in pakchoi under greenhouse conditions before harvest should be extended to 14 days, and the quality of the products will meet the minimum requirement level (MRL) of China. It is important to pay more attention to the pesticide concentration, and find the substitute for chlorpyrifos in pakchoi production．

Key words: chlorpyrifos, greenhouse pakchoi, residue, degradation dynamics, techniques for safe use