The invention relates to a soil body improvement method of rectangular shield construction. The soil body improvement method comprises the following steps of arranging an improved injection hole in each cutterhead spoke of a rectangular shield; carrying out region division on a soil cabin in the rectangular shield to divide the soil cabin into a left region, a right region and an upper region; in the rectangular shield construction, carrying out soil body improvement on foam injected from the improved injection hole; carrying out soil body improvement on bentonite slurry injected from the left region and the right region; carrying out soil body improvement on foam which is continuously injected from the upper region of the soil cabin. The invention provides the applicable soil body improvement method aiming at the rectangular shield construction so that full-section improvement of a cutterhead and the soil body is realized; uniform soil properties and balanced soil pressure in each region are ensured, and the influences on the shield construction by the soil pressure are reduced.