The formation mechanism of metallofullerene Y@C-82 was investigated by ab initio calculations with two theoretical models. The first model is a traditional Y@C-80 + C, "fullerene-road" growing mechanism, in which the Y@C-82 is assumed to form by combining Y@C-80 and C-2 fragments, and the second model involves formation by an unclosed C-76 and a C6Y fragment. The calculated results showed that the second mechanism is much more energetically favorable.