Based on the soil-structure interaction theory， the site containing open trench topographic conditions is decomposed into a near-field system and an infinite-field system using the proportional boundary finite element method. The grid refinement discreti? zation of the near-field region is performed by the quadtree decomposition technique， the displacement unit-impulse response ma? trix is used to represent the interaction forces at the interface between the near-field and far-field intersections. The obliquely inci? dent plane SV wave is transformed into an equivalent nodal force acting on the boundary of the near-field region to simulate the ex? citation of the incident wave on the near-field system， which leads to a numerical model of the elastic wave propagation problem in the time-space domain. Through the numerical example， the validity of the method is verified and the effects of the parameters such as the incidence angle and the depth of the trench on the vibration isolation effect are analyzed. The results show that the vibration isolation effect increases with the increase of the incidence angle； and when the incidence angle is larger， further increasing the depth of the open trench， will make the open trench has a better vibration isolation effect.