In order to reveal the effects of impermeable interlayer on steam assisted gravity drainage（SAGD）production process for dual horizontal well，four physical simulation experiments were carried out. According to the characteristics of SAGD in the dual horizontal well，the dimensionless Subcool was proposed for boundary similarity，which provides a control criterion for physical simulations. A two-dimensional physical model of dual horizontal well SAGD was built based on the reservoir parameters in Mackay River oil sands block. Four experiments were conducted to probe the effect of interlayers on SAGD production. Among them，test 1 was a homogeneous model and served as a basic case and test 2-4 were heterogeneous models with interlayers. The results show that the development of steam chamber in the homogeneous model may be classified into three stages，which correspond to the stages of incremental production，stable production and decreased production respectively. Comparisons among test 1 and test 2-4 indicate that the existence and distribution pattern of the interlayer cause some effects on the development of steam chamber and production performance. It is indicated that the higher the interlayer is located，the less the steam chamber is suffered and the less the production performance is influenced. If there is an interlayer between the injector and the producer，it is hard to form an effective flowing path from the injector to the producer. The single well SAGD（SW-SAGD）technology was proposed as a new preheating method.