The present invention relates to a system and a method for purifying highly contaminated soil by combining stepwise sequential advanced-separation and electrokinetics. More specifically, the system comprises a measuring unit which measures the concentration of heavy metals, a pre-processor, a foreign material removal device installed to screen contaminated soil, at least one multi-stage particle sorter, a hydrocyclone, an electrokinetic device for purifying contaminated soil, a purifier, a filtering device, and a neutralization tank. [Reference numerals] (10) Belt feeder; (11) Drum washer; (12) Disintegration device; (20) Foreign material removal device; (30) Multi-stage particle sorter; (31) Overflow process tank; (41) Surface grinder; (42) Hydrocyclone; (43) Particle sorter; (44) Scum precipitation concentration tank; (51) Coagulation precipitation tank; (52) Concentration tank; (53) Acid-elution tank in first-third steps; (60) Filter press; (61) Neutralization tank; (62) Compression floating tank; (63) Fe(III)-reforming activated adsorption top; (64) Process water storage; (65) Rinsing water storage; (AA) Foreign substances; (BB) Polymer aggregates; (CC) Precipitation concentration tank(1); (DD,EE) Scum; (FF) Precipitation concentration tank(2); (GG) Particle sorter lower tank; (HH) Hydrated lime storage tank; (II) Polymer aggregates; (JJ) Supplementary water storage; (KK) Acid storage tank; (LL) Acid-elution tank in first-third steps; (MM) Filter press(scum); (NN) Contaminated soil, contaminated soil + rinsing process water, contaminated soil + compounds; (OO) Rinsing process water; (PP) Compounds(eluent, polymer aggregates, hydrated lime)