By using the Richards-Wolf vector diffraction theory, the focusing properties of Bessel-Gaussian radially polarized laser beams modulated with a diffractive optical element (DOE) in a 4pi focusing system were investigated which consists of two same high numerical aperture lens. Due to the adjacent ring interference of DOE, the intensity distribution near the focus is different from the intensity distribution without DOE modulation. The results simulated by Matlab show that the multifocal spherical spots can be obtained when Bessel-Gaussian radially polarized beam passes through this optical system. The number of spherical spots is associated with the number of belts of DOE and relative size of adjacent ring. The spherical focal spots can move along the optical axis if the relative phase of left and right of the incident beam is changed. The results show important applications in optical microscopy, optical data storage, and particle manipulations.