Abstract: Fuzzy-ball diverting agent has been applied on site for fracture initiation and diverting, but its mechanical mechanisms of diverting have not been studied yet. In this paper, 7 natural cores (?25 mm) of tight sandstone were adopted in laboratory to simulate the postfrac initial fractures by using artificial fractures. And fuzzy-ball diverting agent was injected into 3 cores to plug the fractures. The radial stress-strain curves of 7 cores were measured by means of the triaxial testing machine. The horizontal stress differential of the cores after they were plugged with fuzzy-ball diverting agent was calculated, and it is 5.33 MPa, which is 37.81% lower than that of the plugged cores, i.e., 8.57 MPa. And the brittleness coefficient of the cores plugged with fuzzy-ball diverting agent drops by 64.44% from 0.45 to 0.16. It is indicated that to adopt fuzzy-ball diverting agent for plugging fractures can increase the overall strength of rock and decrease the horizontal stress differential of rock, so as to provide the mechanical setting for the diverting of new fractures after refracturing. In laboratory, large-size cores of 300 mm×300 mm×300 mm were used to simulate the strata. In the true triaxial fracturing simulation system, the initial fractures were created by using guar, fuzzy-ball diverting agent was injected for temporary plugging and then guar was injected again to simulate the secondary fracturing. The fracturing pressure of secondary fracturing was tested and it is about 10 MPa higher than that of primary fracturing. Finally, the cores were split for qualitative observation. It is shown that the orientation of new fractures created by secondary fracturing after temporary plugging is obviously different from that of initial fractures while the orientation of new fractures in unplugged cores is coincident with that of initial fractures. In conclusion, fuzzy-ball diverting agent can increase the fracturing pressure of rocks with fractures, decrease the in-situ horizontal stress differential and increase the fracture initiation angle of new fractures so as to promote the diverting of fractures.