Electro–elasto–microfluidic technology integrates the high controllability of electric fields with the viscoelasticity of non-Newtonian fluids, representing a frontier approach for precise manipulation of particles at the micro- and nanoscale. However, existing studies have predominantly focused on macroscopic rheological properties and particle size effects, while the influence of microscopic rheological parameters—such as polymer chain length—on particle migration behavior remains insufficiently understood. In particular, the coupling mechanism between the polymer chain length and slip-velocity-induced lift has yet to be elucidated. In this study, an electro–elasto–microfluidic system with tunable viscoelastic parameters was designed, and a control strategy incorporating polymer chain-scale parameters was established to systematically investigate the effects of polymer solutions with different chain lengths and concentrations on the migration of nano- and microparticles. Experimental results demonstrate that the polymer chain length plays a critical role in regulating the lift force balance in electro–elasto–coupled systems. Numerical simulations further reveal that the polymer chain length significantly influences the particle slip velocity. The particle slip velocity U_s exhibits an approximately linear dependence on the ratio between the force acting on the particle and its radius, F_p/R. With increasing polymer chain length, the slip velocity U_s decreases monotonically under identical F_p/R conditions. Theoretical analysis indicates that, as particle size decreases, the flow-induced elastic lift decays much more rapidly than the slip-induced lift, causing the latter to dominate nanoparticle manipulation. Based on these findings, efficient nanoparticle focusing at prescribed flow velocities, as well as high-throughput continuous separation of particles spanning the nano- to microscale, were achieved by appropriately matching polymer chain length and concentration. This work not only elucidates the microscopic regulatory role of the polymer chain length—a key microrheological parameter—on macroscopic particle dynamics, but also provides a new theoretical foundation and design strategy for electro–elasto–synergistically driven microfluidic sorting technologies.