  In our previously published papers, it was argued that a massive non-Abelian
gauge field theory in which all gauge fields have the same mass can well be set
up on the gauge-invariance principle. The quantization of the fields was
performed by different methods. In this paper, It is proved that the quantum
theory is invariant with respect to a kind of BRST-transformations. From the
BRST-invariance of the theory, the Ward-Takahashi identities satisfied by the
generating functionals of full Green's functions, connected Green's functions
and proper vertex functions are successively derived. As an application of the
above Ward-Takahashi identity, the Ward-Takahashi identity obeyed by the
massive gauge boson propagator is derived and the renormalization of the
propagator is discussed. Furthermore, based on the Ward-Takahashi identity, it
is exactly proved that the S-matrix elements given by the quantum theory are
gauge-independent and hence unitary.
