Based on questionnaire survey, this paper establishes a global standard system for downsizing so as to calculate the contribution value of every individual employee, and consequently the number of downsizing. As an abstraction of the process, a mathematic optimization model with constraints has been developed and resolved with genetic algorithms, and a satisfactory result has been achieved by the method. Thus, problem of deciding number of employees to be cut subjectively by enterprise can be avoided. The new model provides managers with a method for deciding the accurate number of lay-offs and who to be cut, so as to maximize the overall interests of the enterprise, enhance rationality of decision-making, and provides reference for managers to improve the accuracy and efficiency of decisionmaking with computer.