Abstract: The effect of metallic pit prop on transmission characteristics in tunnel is studied. A fork waveguide model is proposed and the mode matching and multi-mode network technique are used to analyze the transmission characteristics of rectangular tunnel with metallic pit prop. The change of the reflection coefficient of dominant mode with working frequency, the row number of metallic pit prop, and pit prop diameter are obtained, respectively. The present approach can be used to analyze other discontinuity problems caused by metallic obstacle in rectangular tunnel.