Abstract: There are many substances with similar function of surfactants in plant kingdom,such as saponin,glycolipid,phospholipid,etc,which play important roles in enhancing the solubility of some low water-soluble compounds.In order to reflect the solubility and bioactivity under nature condition of these compounds accurately and faithfully,using surfactants as cosolvents is an effective way in allelopathic bioassay research.However,there are only a few researches on the application of surfactants in plant bioassay and they are lack of safety investigation.In this paper,wheat and cabbage were chosen as test plants for studying the safety of surfactants.The safety concentration of wheat and cabbage are as follows respectively:Tween-80(<0.1%,<1.5%);Tween-60(<0.5%,<4.0%);Tween-40(<0.1%,<6.0%);Tween-20(=0.1%,<0.1%);Poloxamer-188(<8.0%,<4.0%);Myrij52(<1.0%,=0.5%).The safe concentration range of Tween-80,Tween-60,Tween-40 and Poloxamer-188 is wide,and can be used as cosolvents in allelopathic bioassay research.However,the concentration range of Myrij 52 and Tween-20 is relatively narrow,and may not be appropriate as cosolvents.