Ba5RZr3Nb7O30(R=La, Nd, Sm) lead-free relaxor ferroelectrics were prepared by a standard solid-state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba2+ and R3+ in A1 site was observed, while A2 site was only occupied by Ba2+. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel-Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P-E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba5SmZr3Nb7O30. For Ba4R2Zr4Nb6O30 and Ba5RZr3Nb7O30 (R=Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased t(A1), which is a result of cross distribution at A1 site. Compared with Ba5RTi3Nb7O30, Zr substitution at B site enhances the relaxor nature.