Abstract:In order to construct quantitative alarm system instructing the control method of the pests of urban green, this paper took hazards of urban green plant pests as one of the important natural calamities and risks, and based on indexes of risky resource, risky sign and risky case, the methods of constructing early-warning index system including 36 indexes of Parasa consocia Walker were put forward. The factor could be measured for risk by 1 to 5 grades with the methods of fixed quantity or qualitative analysis. Using P.consocia in Nanhui District of Shanghai City circling greenbelt as an example, the result showed that each factor index of risky resource, risky sign and risky case was 25.9, 28.3 and 27.4, respectively. The integrated calamities of the 2nd generation of P.consocia in 2006 suited for middle risk with the index 81.6 and yellow alerts should be delivered.