It features very important significance to determine dQ's signs and calculate dQ's quanti-ty, which belong to an arbitrary elementary process of quastistatically thermodynamic pro-cess of perfect gas. The presentation of the significance is not only in the theoretical realm,but also in practical scope (e, g, general discussion of cycle efficiency for real heat engine).In accordance with certain mode, this paper purposes to put forward generally effectivemethods dealing with dQ, namely dQ≥0 or dQ
