Ground state energy of anharmonic oscillator in the strong limit coupling

Non-perturbative calculation method, allowing one to obtain good numerical results within the limit of a strong coupling, is formulated, taking the quantum-mechanical oscillator basic level energy calculation as an example. The consideration is made on the base of functional integral formalism allowing one to uniformly formulate both quantum-mechanical and field-theoretical problems. This fact points out to a substantial universality of the method proposed