Urban ventilation or wind environment focus on the air flow distribution and pollution dispersion which are studied by the tools of wind tunnel and computational fluid dynamics (CFD) simulation. The latter is easy to be employed, but its reliability is under suspicion due to the high uncertainty of air stream. In the city, the sheltering among buildings affects each other in air flow, and the basic element is the two-building model. Shade problem between the two buildings are divided into upstream building with a hole (such as drafts) with no hole two situations, Reynolds average model of using CFD (RANS) simulation of wind pressure on the surface of the building downstream, and compared with wind tunnel experiments are strictly, to discuss the CFD method in question the reliability of the basic unit. The analysis of grid sensitivity states that the smallest side length of the cell around 2% of building height is sufficient to obtain steady results. The comparison of five typical RANS model presents:the reliability of RANS model to the upstream with hole occlusion was significantly higher than that of simulation without hole occlusion; estimations on upper parts of building are more accurate than on lower parts; the SST k-ω model can acquire best results with error of 11% in porous interfering building, and with 16% in sealed one, in comparison of experimental data.