Data of neutron monitors for different solar magnetic cycles have been used to study the role of the regular and stochastic components of the interplanetary magnetic field (IMF) on the diffusion propagation of galactic cosmic rays (GCR). Two classes of GCR variations are considered. The first one is the 11-year variation of GCR related with the similar periodic changes in solar activity and solar wind parameters; the second one is the quasi-periodic 27-day variation stipulated by the heliolongitudinal asymmetry of the electro-magnetic conditions (e.g. solar wind velocity and diffusion) in the inner heliosphere caused by the Sun's rotation. Transport equation of GCR particles has been numerically solved for two and three dimensional IMF including diffusion, convection, drift due to gradient and curvature of the regular IMF and the energy change of GCR particles because of interaction with the irregularities of solar wind. It is shown that a significant changes in the structure of the IMF's irregularities from the minima to the maxima epochs of solar activity reflecting in the dependences of the diffusion coefficient on the GCR particles' rigidity is one of the general reasons of the 11-year variation of GCR. The heliolongitudinal asymmetries of the solar wind velocity and diffusion processes in the inner heliosphere cause the GCR 27-day variation with the larger amplitude in the minima and near minima epochs of the qA>0 solar magnetic cycle, than that in the qA<0 cycles due to existence of the oppositely directed drift streams of GCR. An interpretation of this phenomenon has been proposed based on the modern theory of GCR propagation.

PACS numbers: 96.50.Ci, 96.40.Cd