Steam injection is one of the most effective methods to develop heavy oil reservoirs. Steam overlap is a common phenomenon because of the density difference between steam and crude oil. The steam overlap characteristics of the heavy oil reservoir were intuitively described by 3D physical simulation experiments. The pressure，temperature field and fluid production under different perforation modes were analyzed during the steam flooding. The experimental results reveal that the main steam sweep area is at the top of the reservoir when the injection well is uniformly perforated. As the injection time increases，the central reservoir begins to absorb steam gradually and the remaining oil mainly gathers at the bottom of the reservoir. When the injection well is selectively perforated，the temperature difference between the top and bottom reservoir decreases and the steam absorption of the bottom zone increases obviously. As a result，the producing degree and oil recovery are enhanced. On this basis，the numerical simulation method was used to optimize the selective perforation plan for the injection and production wells. The results show that the selective perforation can effectively control the steam overlap.It is optimal that 1/3 of the lower reservoirs and 1/2 to 2/3 of the lower reservoirs are perforated for the injection wells and production wells respectively.