Abstract： Fairness is a comprehensive strategy that takes into consideration of self-interest and other people's interests. The development of fairness norms, that is, using certain rules to distribute resources among different agents, includes two levels: the cognitive level, understanding fairness norms, and the behavioral level, applying fairness rules. Young children endorse fairness norms related to resource distribution, but often act in contradiction to those norms when given a chance to distribute. While currently most research focuses on children's fairness cognition or behavior, the phenomenon of children’s fairness cognition-behavior gap and its influence factors have rarely been explored in the context of a single study. Using a novel approach, the present study aims to investigate the gap of fairness cognition and behavior among 4- to 8- year-old children. The research presented here offers clear evidence of this discrepancy and goes on to examine possible explanations for its diminution with age, as well as the impact of social comparison on such resource distribution behavior. Study 1 adopted the Dictator game to examine the equity principle among 105 4~8-year-old children’s fairness cognition and behavior, and compared the cognition-behavior gap. The justifications/motivations of children’s distribution behavior were also coded and analyzed. In Study 2, We replicated the findings in Study 1, that children will take a cost to avoid being at a relative disadvantage, but also found that 5-to 6-year-olds would spitefully take a cost to ensure that another welfare falls below their own. We tested 80 6-year-old children, and analyzed the influence of social comparison on children’s distribution behavior, both upward and downward social comparisons considered. A variant of the Dictator Game, were used to investigate children’s behavior in different conditions. In Study 1, we found that children at this age already have developed fairness understanding, their fair distributive behavior increased with age, and the gap between cognition and behavior decreased with age. Nevertheless, they failed to engage in equal distribution until age 8. Children’s interpretations of their behavior showed a significant age-related difference from 4 to 8. As children grew older, their interpretations transitioned from focusing on desire to principle. Study 2 found that the degree of unfairness and the cost had a significant impact on the choice of distribution behavior in both the upward social comparison and downward social comparison. Under the no-cost situation, children were more inclined to avoid their own disadvantage and to favor their own favorable results. In the highly unfair situation, it was necessary to avoid being inferior to others, even if the cost was too high. The present study of children’ fairness cognition-behavior gap in a single environment contributes to the literature on moral development. The results provide some support for traditional accounts of moral development by showing that, in the course of development, children’s distribution behavior is increasingly consistent with the norm of fairness that they endorse from an early age. These results also suggest that social comparison influences children’s distribution behavior, and that the development of fairness includes overcoming an initial social comparison preference for self-advantage/disadvantaging others.