The government's function for social governance is increasingly essential in the risk society. Major Decisions Assessment on Social Stability Risk (MDA-SSR) is to measure and acknowledge the extent of social stability risk threat from major decisions. This essay is aiming at improving policies effects of MDA-SSR so as to form a scientific and nonnative regulation on "the assessment subject" (AS). Using the method of evaluable assessment, this paper firstly analyzes the current mode of AS and then evaluates deeply the policies of assessment subject. It finds out that there are three problems that leading to low-perfonnance of MDA-SSR, namely that, unscientific policy arrangement, shortage of supportive policies, and poor-complete supporting systems. Hence, China should refine policies' goal of MDA-SSR on AA, in order to improve policies effects. Firstly, detail the category of major policies, and determine the source of assessment subject. Secondly, formulate provision of procedure, and increase financial input on policy evaluation. Thirdly, regulate outsourcing payment, and stimulate multiple subjects' participation.