While few-layered graphene (FG) has been synthesized by several different arc-discharge methods, its growing mechanism has hardly been studied by experiment. Here, we have investigated systematically its growth mechanism using the arc-discharge method under different environments including helium, oxygen-helium and hydrogen-helium. The results indicate that FG can only be produced in the presence of reactive gases, implying that the growing mechanism of few-layered graphene involves graphite evaporation and reactive-gas-confining crystallization of the evaporated carbon clusters. The key factor inducing the discrepancies in FG synthesis under different buffer gases can be assigned to the reactivity of corresponding gases.