Abstract: The horizontal permeable reaction barrier (HPRB) is a passive remediation technology for the volatile organic compound (VOC) vapor in the vadose zone. It has the advantage of consuming less energy during the operation. And it can be used as a long-term risk control measure for the large-scale VOC contaminated sites. A transient analytical model is proposed in this study to simulate the VOC vapor migration in the layered soil containing a layer of the HPRB. The Laplace transformation is adopted to derive the general solution in the Laplace domain, and then the Laplace inversion of the numerical Talbot method is adopted to derive the semi-analytical solution of the VOC vapor migration. It is found that the HPRB is more suitable for the contaminated sites with low effective diffusivity soil. The large depth of the HPRB is not conducive to the removal of the VOC vapor. The increase of thickness of the HPRB enhances the removal of the VOC vapor. The increase of the source concentration decay rate can reduce the peak value of the VOC concentration in the contaminated sites. The neglect of the source decay can lead to the excessively conservative design of the HPRB. Finally, the design procedure of the depth and thickness of the HPRB is proposed.