  A new method for non-perturbative calculation of Green functions in quantum
mechanics and quantum field theory is proposed. The method is based on an
approximation of Schwinger-Dyson equation for the generating functional by
exactly soluble equation in functional derivatives. Equations of the leading
approximation and the first step are solved for $\phi^4_d$-model. At $d=1$
(anharmonic oscillator) the ground state energy is calculated. The
renormalization program is performed for the field theory at $d=2,3$. At $d=4$
the renormalization of the coupling involves a trivialization of the theory.
