Defence strategy of any country is one of the most important necessities for maintaining national security which has an effective role in security which has an effective role in securing national inferests of that country. A comprehensive defensive strategy contains two dimensions: operating defence and passive defence. Operating defence and passive defence. Operating defence's application is in military field and the passive defence application not only is in military, but in the social, economical, political and cultural fields as well. The passive defence is divided in two parts of hard and soft which each part has its particular bases. The article's goal is, by using descriptive research method, first, to define the passive defence, indicates its variety and foundations, and second, determines the capability of the soft passive defence facing with a soft war in the framework of a defensive strategy.