Abstract: Sustained casing pressure (SCP) is a common issue at high temperature, high pressure, and high sour gas fields. It will lead to serious threats to the safety of gas well production. It is very important and imminent to determine the risk level of the well. Based on international standards and the reasons of well losing integrity, 30 parameters affecting gas well integrity are proposed. And the influence of each parameter is evaluated respectively. Based on the combination of field experience and theoretical research, the single well scoring criterion and the model of evaluating well risk level are established. According to the risk evaluation model, the wells can be divided into 3 categories, Ⅰ, Ⅱ, and Ⅲ. Emergency measures need taking immediately for Type Ⅲ wells. The production characteristics and treating technologies can determine the possibility and severity of integrity losing. The current state is the most important parameter to evaluate the well integrity. The annulus pressure and leaking rate can be viewed as one-vote negation parameters.