The invention relates to a method for treating a soft foundation. The method comprises the following steps of: 1, inserting electrical bars into treated soft soil; 2, reserving vertical drainage channels in the treated soft soil and communicating the vertical drainage channels with vacuum-pumping equipment; and 3, starting up the electrical bars to heat the treated soft soil and simultaneously starting up the vacuum-pumping equipment to vacuumize for quickening the drainage of bound water of the treated soft soil. The invention also relates to another method for treating the soft foundation. The method is implemented by arranging the electrical bars in sand drains. Due to the adoption of the method, the bound water in the soft soil can be gasified so that the bound water is quickly drained out of the soft soil, and the difficult problem that the water content of the soft soil is difficult to be lower than the critical point of 35 percent is solved. The method effectively reduces the bound water of the soft soil, realizes controllable improvement of mechanical properties of the soft soil, and meets the requirements of engineering construction by controlling heat energy and heating time. Due to the adoption of the technical scheme of the method, the time limit for a project can be shortened by over 50 percent, the construction cost can be saved by over 30 percent, the quality can be greatly improved, and the construction is environmentally protective.