The effects of He, Ar and N2, as the working gas, on the formation of Fullerenes were studied respectively. The experimental results indicated that the different inert gases greatly affect both the productivity and the composition of Fullerenes and for the same gas the different pressures also affect the productivity. It was also found that no Fullerenes can be obtained without a working gas. It indicates that the gas of a difinite pressure may be necessary to the formation of Fullerenes. A new possible mechanism of the Fullerenes formation was suggested.