Shale barrier distributes widely in heavy oil reservoirs. However, the influence mechanism of shale barrier on heavy oil recovery is still unclear. For this reason, the influence mechanism in physics was first proposed. Then, the influence mechanism in mechanics was concluded from the steam migration velocity decreasing and the heat conduction rate enhancing. Especially, it was obtained by theoretical analysis that shale barrier has a positive effect on heavy oil recovery under the reasobale condition. To validate the influence mechanism, a numerical model containing the shale barrier was established. The numerical results validated the influence mechanism in physics from two aspects of steam chamber shape and migration behaviors of steam and oil. In addition, the numerical results showed that it has the higher cumulative oil volume and the lower residual oil saturation for the heavy oil recovery when considering reasonable distribution of shale barrier, validating the conclusion that shale barrier has a positive effect on heavy oil recovery. Additionally, the reason behind positive effect caused by the shale barrier was analyzed, including the longer production period, the higher steam injection volume and the lower heat loss. Especially, economic feasibility for heavy oil recovery was evaluated by calculating net present value (NPV) and the ratio of the produced energy to the consumed energy. Finally, the parametric analysis was performed to investigate effects of geometric properties of shale barrier on heavy oil recovery, including the barrier location, the barrier length, the barrier thickness and the number of barrier. The results show that: (1) the reasonable distribution of barrier location far away from the injection well is advantageous for the heavy oil recovery; (2) the reasonable increasing of barrier length, thickness and number is beneficial for the heavy oil recovery. ►Influence mechanism of shale barrier on heavy oil recovery using SAGD was proposed.►Influence mechanism was validated by numerical model considering shale barrier.►Shale barrier has, to some extend, a positive effect on heavy oil recovery using SAGD.►Shale barrier induced potential benefits for the heavy oil recovery were concluded.