Task factoring to shortest of task completion time among local resources and cloud computing resources is the cloud users optimized decision problem, if cloud users can use the aforementioned two resources at the same time, and this paper studies cloud users optimal task factoring decision. Because of the sharing characters of cloud computing resources, users decision-making will affect the task completion time of the rest users, and so solving the Nash equilibrium strategy to analyze the users’ behavior and to determine the optimal decision-making are proposed. Nash equilibrium is solved when the two types of users with big tasks and small tasks are adopted, and the cloud users’ optimal decision is proposed through simulation when different ratio of big and small tasks’ workload, different ratio of local and cloud execution speed, and different probability of big task users are given respectively.