  We prove several approximation theorems of the complex Monge-Ampere operator
on a compact Kahler manifold. As an application we give a new proof of a recent
result of Guedj and Zeriahi on a complete description of the range of the
complex Monge-Ampere operator in the class of w-plurisubharmonic functions with
vanishing complex Monge-Ampere mass on all pluripolar sets. As a by-product we
obtain a stability theorem of solutions of complex Monge-Ampere equations in
some subclass.
