  The development of an analytically iterative method for solving steady-state
as well as unsteady-state problems of cosmic-ray (CR) modulation is proposed.
Iterations for obtaining the solutions are constructed for the spherically
symmetric form of the CR propagation equation. The main solution of the
considered problem consists of the zero-order solution that is obtained during
the initial iteration and amendments that may be obtained by subsequent
iterations. The finding of the zero-order solution is based on the CR isotropy
during propagation in the space, whereas the anisotropy is taken into account
when finding the next amendments. To begin with, the method is applied to solve
the problem of CR modulation where the diffusion coefficient $\kappa$ and the
solar wind speed $u$ are constants with an Local Interstellar Spectra (LIS)
spectrum. The solution obtained with two iterations was compared with an
analytical solution and with numerical solutions. Finally, solutions that have
only one iteration for two problems of CR modulation with $u = constant$ and
the same form of LIS spectrum were obtained and tested against numerical
solutions. For the first problem, $\kappa$ is proportional to the momentum of
the particle $p$, so it has the form $\kappa=k_0\eta$, where
$\eta=\frac{p}{m_0c}$. For the second problem, the diffusion coefficient is
given in the form $\kappa=k_0\beta\eta$, where $\beta=\frac{v}{c}$ is the
particle speed relative to the speed of light. There was a good matching of the
obtained solutions with the numerical solutions as well as with the analytical
solution for the problem where $\kappa = constant$.
