Abstract: Experiments on the induced endurance of cucumber were carried out by application of several chemical materials separately to the root from the beginning of cotyledon stage.The results showed that regardless of the natural or artifical induced diseases,the decrease of the diseased plant rate was significant after induced at the root with several chemical materials.The results from analysing the chemicals that could possibly induce immunity indicated that ammonias,benzenes and potassium chloride were closely related to the induced resistances of cucumber leaves to downy mildew.