Abstract: Aqueous solutions of BTH、SA、BABA、Oxalic acid and KCl were used on seedling with two true leaves 2 days before inoculation with P. cubensis. Results obtained showed t these inducer all could induce resistance in cucumber against downy mildew except KCl. The better inducer in the study were BTH and oxalic acid and their optimum induction concentration were 0.5 mmol/L and 10 mmol/L respectively. Expression of resistance in the leaves after BTH or oxalic acid treatment continued for at least 15 days. The combination of BTH with oxalic acid or BABA did not more significantly increase the induce effect than simple inducer.