Abstract: Two sampling units (plant and quadrat) and two sampling methods (random and fixed) were adopted to compare the variation degree of the diversity of arthropod communities in different chinese cabbage fields. The results show that a lower variation degree was found when the random sampling method was adopted with quadrat (0.11m²) as sampling unit at seedling stage and with plant as sampling unit from growing to mature stage.The community diversity was relatively steady,when the critical number of samples was more than 12 quatrats (0.11m²) at seedling stage,30 plants in growing period,and 20 plants at mature stage.The optimum sampling unit,sampling method and sampling number of arthropod diversity in leafy vegetable field were also determined.