  Spin interactions in relativistic quark-antiquark system in magnetic field is
considered in the framework of the relativistic Hamiltonian, derived from the
QCD path integral. The formalism allows to separate spin-dependent terms from
the basic spin-independent interaction, contained in the Wilson loop, and
producing confining and gluon exchange interaction. As a result one obtains
relativistic spin-spin interaction $V_{ss}$, generalizing its nonrelativistic
analog. It is shown, that in large magnetic field $eB, V_{ss}$ modifies and
produces hyperfine shifts which grow linearly with $eB$ and preclude the use of
perturbation theory. We also show, that tensor forces for $eB \neq 0$ are
active in all meson states, but do not grow with $eB$
