The invention discloses a construction method for a soft soil foundation. The construction method comprises the following steps that 1, foundation flattening is conducted; 2, a prefabricated hole witha predetermined depth is formed; 3, a deep mixer is used and rotates, cuts soil and sinks simultaneously around a reserved pile, after the deep mixer sinks to the designed depth, reverse rotating isconducted for lifting, meanwhile, cement paste capable of forming pervious concrete is injected into the soft soil, paste spraying and stirring are conducted simultaneously, and thus the cement pasteand the soil are stirred fully until reaching the ground, and the cement paste contains a curing agent; 4, stirring for sinking, reverse rotating for lifting and paste spraying are repeated until pile-forming is achieved, and a deep stirring pile is formed; 5, the reserved pile is pulled out, a drainage well is formed on the deep stirring pile; 6, the above steps are repeated, and the multiple deep stirring piles with the drainage wells are formed on the foundation; and 7, pre-pressure drainage consolidation is conducted on soil layers between the piles through the drainage wells. According tothe construction method for the soft soil foundation, the deep stirring piles are formed, and meanwhile, the deep stirring piles further have the function of the drainage wells, so that vacuum pre-pressure drainage consolidation treatment is conducted on the soil layers between the piles more conveniently.