rational principle of cost-benefit is often regarded as the basic norms of behavior. But further research found that rational decision and rational implementation is not uniform, there is a gap between knowledge and practice. This is because the decision needs rationality, implementation also needs rationality, but rationality is limited. Therefore, rational limitations embodied in two aspects of cognitive constraints and limited executive power. Due to limited capacity of rational implementation, principle of least effort is more effectively than rational principles to explain repetitive behaviors. Lack of chronic disease prevention behavior is not just due to the limited cognitive rationality, and the limited capacity of rational implementation is too. Increasing individual awareness and action capacity are important measures to address lack of chronic disease prevention behavior.