The invention provides a method for lateral confinement disintegration test of an extremely soft rock. The method comprises the following steps: 1, sampling: performing onsite sampling by adopting a cutting ring, and producing a cutting ring sample indoors; 2, drying the cutting ring sample: drying the cutting ring sample placed on a tray in an oven at a temperature being not less than 20 DEG C until the cutting ring sample has a constant weight, taking out the cutting ring sample, placing the cutting ring sample in a drier, cooling the cutting ring sample to room temperature, and weighing thecutting ring sample; 3, immersing the cutting ring sample in water: slowly adding water into the tray until the water level height is flush with the upper surface of the cutting ring sample, standingthe sample for 24 h, observing the disintegration phenomenon, and shooting the disintegration; 4, screening the sample: completely drawing the water out of the tray, standing the tray in the oven for24 h, taking out the tray from the oven, cooling the sample to room temperature, taking out the sample from the cutting ring by using a sampler, screening the sample through standard sieves with theapertures being 60 mm, 40 mm, 20 mm, 10 mm, 5 mm and 2 mm respectively, and weighing the screened sample to obtain the mass of disintegration products having different apertures; and 5, calculating and analyzing the disintegration rate.