The correlative method of unsymmetrized self-consistent field (CUSF) is used to study dynamical characteristics of a strongly anharmonic crystal with body-centered cubic lattice, namely, the inter-atomic and mean square relative displacements. We present the general formulae for crystals with anharmonicity, including the strong one, up to fourth anharmonic terms. Taking into account the second order of the method we calculate correlations in this lattice between the nearest, second, third, fourth and fifth neighbors. The influence of more distant interactions is discussed. The results are compared with those obtained previously for an weakly anharmonic BCC crystal. We use the Schiff potencial for Na and also Lennard-Jones potentials for comparison.