The extremely fractured surrounding inside have many internal microcracks, which are easily broken under external forces. When the generalized Hoek-Brown strength criterion is used to describe the extremely broken surrounding rock, the influence of breakage effect on the strength cannot be considered. In order to investigate the influence of particle breakage on the strength criterion, five different gradations of extremely broken phyllite samples were used to conduct large shear and sieving tests to determine the particle breakage rate of samples. The relationship between the breakage rate and the surrounding rock stress was obtained. The breakage ratio was introduced into the Hoek-Brown strength criterion in the form of damage content, and the Hoek-Brown strength criterion considering the breakage effect was established. By comparing the two strength criterion envelopes considering and not considering the particle breakage effect, it is known that when the surrounding rock pressure is greater than 2 MPa, the strength envelope begins to separate. The greater the surrounding rock pressure, the more obvious the influence of the breakage effect on the rock strength. By continuously increasing the stress state, it is concluded that when the surrounding rock stress is high (> 500 kPa), the strength envelopes of the Hoek-Brown strength criterion considering and not considering the breakage effect begin to separate significantly. The calculation results of the Hoek-Brown strength criterion considering the breakage effect are closer to the test results, and the modified Hoek-Brown strength criterion is more suitable for the extremely broken surrounding rock.