  Quantum radiation properties of Dirac particles in general nonstationary
black holes in the general case is investigated by both using the method of
generalized tortoise coordinate transformation and considering the asymptotic
behaviors of both the first and second order forms of Dirac equations near the
event horizon. It is generally shown that the temperature and shape of 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 missing in that of
scalar particles. Also, we reveal a relationship that is ignored before between
thermal radiation and non-thermal 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
non-thermal radiation for general nonstationary black holes.
