  We present a theory based on Green's function formalism to study magnetism in
disordered Heisenberg systems with long range exchange integrals. Disordered
Green's function are decoupled within Tyablicov scheme and solved with a CPA
method. The CPA method is the extension of Blackmann-Esterling-Beck approach to
system with environmental disorder term which uses cumulant summation of the
single-site non crossing diagrams. The crucial point is that we are able to
treat simultaneously and self-consistently the RPA and CPA loops. It is shown
that the summation of s-scattering contribution can always be performed
analytically. While the p,d,f .. contributions are difficult to handle in the
case of long-range coupling. To overcome this difficulty we propose and provide
a test of a simplified treatment of these terms. In the case of 3D disordered
nearest-neighbor Heisenberg system, a good agreement between the simplified
treatment and the full calculation is achieved. Our theory allows in particular
to calculate the Curie temperature, the spectral functions and the temperature
dependence of the magnetization of each constituant as a function of
concentration of impurity. Additionally it is shown that a virtual crystal
treatment fails even at low impurity concentration
