Quantum　radiation　properties　of　Dirac　particles　in　general　nonstationary　black　holes　in　the　general　case　are　investigated　by　both　using　the　method　of　generalized　tortoise　coordinate　transformation　and　considering　simultaneously　the　asymptotic　behaviors　of　the　first-order　and　second-order　forms　of　Dirac　equation　near　the　event　horizon.　It　is　generally　shown　that　the　temperature　and　the　shape　of　the　event　horizon　of　this　kind　of　black　holes　depend　on　both　the　time　and　different　angles.　Further,　we　give　a　general　expression　of　the　new　extra　coupling　effect　in　thermal　radiation　spectrum　of　Dirac　particles　which　is　absent　from　the　thermal　radiation　spectrum　of　scalar　particles.　Also,　we　reveal　a　relationship　that　is　ignored　before　between　thermal　radiation　and　nonthermal　radiation　in　the　case　of　scalar　particles,　which　is　that　the　chemical　potential　in　thermal　radiation　spectrum　is　equal　to　the　highest　energy　of　the　negative　energy　state　of　scalar　particles　in　nonthermal　radiation　for　general　nonstationary　black　holes.