Abstract Cucumber downy mildew is a rather serious plant disease damage in every place of world. The starting and prevailling of the disease relate closely to its environmental temperature. It can be prevented by proper high temperature condition, because the producing, growing and damaging of the disease spores can be inhibited by high temperature. The dates of starting and prevailling of the disease can be postponed and the damaging degree can be mitigated obviously by using an high temperature control way: raise air temperature in the plastic cucumber shed up to 40—47℃ by closing the door and air-inlet at about noon, last it more than two hours, and then, open the door and air-inlet for "change air" and do it every second day. This preventing way can make the cucumber production increased about 45 per cent and it is more efficent than others.