Multi-scale Eastward-Moving Southwest Vortex (EMSV) inducing severe rainstorms frequently occurs in the middle and lower reaches of Yangtze River Basin (YRB). The Second-Step Terrain Region (SSTR) located in the middle reaches of YRB have significant role in strengthening this synoptic system. This paper systematically studies the topographical effect of SSTR based on the WRF synthetic simulation of three multi-scale EMSV cases that occurred in 2015 and 2016. Results show that the compound circulation simulated by WRF can be decomposed into the meso-scale balanced circulation and the local-scale perturbed circulation with the application of the Piecewise Potential Vortex Inversion (PPVI) technique. The cyclonic perturbed circulation has a closer relationship with the occurrence of local heavy precipitation compared to the balanced circulation. Moreover, the good agreement between the positive Potential Vortex (PV) anomalies and the cyclonic perturbed circulation suggests that the persistence of the cyclonic perturbed circulation highly depends on the positive PV anomalies. Besides, the qualitative sensitivity experiments reveal that the topographical effect stimulates the genesis of the positive PV anomalies mainly by strengthening the latent heat release associated with the updraft, and the latent heat release associated with the cyclonic eddy. The quantitative diagnosis of the source of the PV anomalies shows that the former one contributes more to the genesis of the positive PV anomalies than the latter one. Further quantitative diagnosis of the updraft reveals that the topographical lifting effect is identified as the main mechanism in strengthening the updraft within the topography region