Social stability risk assessment for government' major decision-making，as an important decision-making mechanism firstly developed from local innovation and then institutionalized by central authority，has been evolving for a decade. This evolving process can be regarded as a kind of policy diffusion process，in which the diffusion mechanisms including policy learning，coercion，and imitation function. Comparative analysis based on 69 local policy texts indicates that the policy learning and imitation were more likely to appear in horizontal diffusion，while coercion were more important in vertical diffusion although in which learning and imitation can also be found. Recommendations on improving the social stability risk assessment based on above research findings are represented.