  The energy interval $ (3S-1S) $ in muonic hydrogen is calculated on the basis
of quasipotential approach in quantum electrodynamics. We take into account
different corrections of orders $\alpha^3\div \alpha^6 $, which are determined
by relativistic effects, the effects of vacuum polarization, nuclear structure
and recoil, as well as combined corrections including the above. Nuclear
structure effects are expressed in terms of the charge radius of the proton in
the case of one-photon interaction and the proton electromagnetic form factors
in the case of two-photon exchange interaction. The value of the energy
interval (3S-1S) can be used for a comparison with future experimental data and
determining the proton charge radius with greater accuracy.
