The rapid epidemic spread of SARS have aroused the great attention to the efficient treatment and preventive measure to urban emergent hazard. China is one of the minorities of countries in the world which suffered from severest damage caused by natural disasters now and then. Hazard and accidental event

once they happen in a city

will immediately cause huge economic losses and negative social effect. The fragility of Chinese cities to calamities has become evident. Outburst epidemic disease

leakage of poisonous substance and large area of power or water cut in cities arc commonly happening catastrophes

which will result in social scare

casualty and direct economic losses. Human beings have developed a set of concept and measure of disaster prevention and mitigation in the perpetual struggle with natural calamities. Early-warning of hazard is one of the hot issues of research nowadays. Even for those developed countries

however

the early-warning of an unprecedented outburst hazard like SARS is not an easy task. The author found from the research that the early-warning release of an outburst hazard is a key of effective treatment of it

which requires a consummate early-warning mechanism and early-warning engineering. The five kinds of principle arc to be established

which are principle of humanitarianism

giving prior ity to prevention

legal duty

the first instant response and insurance compensation. The principle of humanitarianism refers to that all the contents and objectives of hazard reduction system should intensively show high respects of human life and nature. The principle of giving priority to prevention emphasizes relying on the construction of "preventive culture" to realize early-warning and achieve ideal hazard suppress effect for a sudden catastrophe. The principle of first instant response is the quick response to a sudden hazard by applying modern science and technology

thus acquiring the longest possible early-warning time and accurate information. The benefit of early-warning lies in responding a hazard at first instant. Fortifying the purpose of modern early-warning engineering and the non-engineering measures of modern early-warning provides a view on premise of humanitarianism. Modern early-warning engineering should display the five characteristics of digitalization of technology and totalizing of clients.