Electric fields have great potential to control meso-scale structures, typically bubbles and agglomerates in gas-solid fluidized beds. However, previous research only considered the effects of polarization forces and ignored the electrostatic effects. This work, by means of cold model experiments, for the first time investigates the effects of DC electric fields on meso-scale structures in a 3-D fluidized bed with electrostatic effects. Results show that particles will also experience the Coulomb force under the effects of electrostatics besides of polarization forces, and the effects of these two electric field forces are different. The Coulomb forces make particles migrate at lower field strengths, then increases the bubble size and breaks up agglomerates. While at higher field strengths, the polarization forces result in formation of agglomerates and reduction of bubble size. Therefore, the effects mechanism of electric fields is the competition effects between the Coulomb force and the polarization forces. The critical transition field strength, at which the predominant position of Coulomb and polarization forces on bubbles and agglomerates changes, is significant in the control of meso-scale structures by DC electric fields.