In this paper, the nucleation and growth characteristics of graphene fabricated on copper foils by low pressure chemical vapor deposition in both conventional growth chamber and vapor trapping chamber were comparatively studied via adjusting the flow rate of CH4. The results indicate that the nucleation density of graphene in the vapor trapping chamber decreases three orders of magnitude than that in the conventional growth chamber and graphene nucleus could grow up rapidly. Meanwhile, the vapor trapping chamber was in favor of the fabrication of perfect graphene domains by providing a stable growth environment. By supplying adequate effective activated carbon atoms, the rate of jointing process of graphene domains in the vapor trapping chamber could be accelerated, bettering the quality of graphene film. On the basis of the experimental results, the mechanism of the vapor trapping chamber impacting the nucleation and growth of graphene was discussed as well.