The softening and disintegration of surrounding rocks at the palm face of tunnels under extremely high ground stress conditions can cause a series of engineering problems. The softening and disintegration law of soft rock expansive rocks was revealed through the disintegration test study of three representative rock samples. The results show that: the disintegration index of soft rock swelling rocks decreases as a function of the number of cycles; the type and content of mineral composition of soft rock swelling rocks are the main factors affecting the strength of disintegration; the disintegration of matrix type and filling type rock samples is mainly caused by water absorption and swelling of hydrophilic minerals, and the disintegration index tends to 5% and 25% respectively after 5 cycles; the disintegration of contact type rock samples is mainly caused by the breakage of cementation bonds, and the disintegration index is about 80% after 5 cycles. The disintegration index is about 80% after 5 cycles, and the disintegration is weak; the change of the content of the particle size group less than 0.25 mm and more than 5 mm can be taken as the limit particle size for the strong and weak disintegration of the soft rock swelling.