Quantum　radiation　of　general　nonstationary　black　holes　is　investigated　by　using　the　method　of　generalized　tortoise-coordinate　transformation　(GTT).　It　is　shown　in　general　that　the　temperature　and　the　shape　of　the　event　horizon　of　this　kind　of　black　holes　depend　on　time　and　angle.　Further,　we　find　that　the　chemical　potential　in　the　thermal-radiation　spectrum　is　equal　to　the　highest　energy　of　the　negative-energy　state　of　particles　in　nonthermal　radiation　for　general　nonstationary　black　holes.　Copyright　(C)　EPLA,　2009