Abstract: It is difficult to improve high plasticity soft soil with conventional drain consolidation methods such as vacuum preloading or surcharge preloading. Large scale laboratory test was conducted to study the feasibility of improving this kind of soft soil with vacuum preloading combined electroosmotic. The vacuum preloading was used to improve the soft soil firstly. When the consolidation degree reached 80%, the electroosmotic started. The current, electric potential and surface settlement was monitored in the test. The result revealed that pole reversal and intermittent current were effective to improve the efficiency of the power. After the test, the strength of the soil increased from 0-0.7 kPa to 18.2-26.2 kPa and the electroosmotic was very helpful to improve the strength in the later stage of the test.