The invention discloses a slant-slip-fault simulating device. A fixed disc model box of the slant-slip-fault simulating device is fixed onto a cuboid pedestal, a dislocation disc model box is movably arranged on prism pedestals, and the fixed disc model box is aslant matched with one side of the dislocation disc model box and communicated with the side of the dislocation disc model box to form a cavity for containing a soil model; slant guide rails are arranged on the slopes of the prism pedestals, and triangular sliding blocks are fixed to the bottom end of the dislocation disc model box and slide along the slant guide rails under the effect of jacks so that the dislocation disc model box can be pushed to be aslant dislocated relative to the fixed disc model box; internally-arranged air bags are arranged in the fixed disc model box and the dislocation disc model box respectively and apply vertical pressure to the soil model. The invention further discloses a simulating method based on the device. The vertical displacement component and the horizontal displacement component of two discs of a slant slip fault can be simulated at the same time, the proportion of the bidirectional displacement components can be changed, and the damage, caused by the slant slip fault, to an underground structure can be truly simulated.