Abstract: Matrix effects and their influencing factors in the determination of 36 pesticide residues in 9 green leafy vegetables by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) were studied. The effects of different sorbents on matrix effects of the QuEChERS method were compared. And three different cleanup methods including QuEChERS, solid phase extraction on an amino column and no cleanup were comparatively evaluated. The results showed that the cleanup efficiency of PSA was better than other sorbents and was able to adsorb impurities from green leafy vegetables. QuEChERS method was better than the other two methods. After the sample was cleaned-up using QuEChERS method, matrix effects of 36 pesticides were negligible in malabar spinach, leaf lettuce, amaranth leaves, water convolvulus and lettuce, which indicated that they could be quantified using the solvent standards. For some pesticides with strong matrix effects, using matrix-matched standards was a good suggestion, and the dilution method could be used to eliminate the matrix effects if the sensitivity is high enough.