Abstract: As for the tunnel reflection tomography (TRT), receiving points only within 10 channels can be installed and used for inversion, and due to destruction in installation, the numbers of effective receiving points are often less than 10 channels, which seriously affects the work progress and greatly limits the practicability of the instrument. In view of this, the travel time formulae for the direct wave and reflected wave of observing system on tunnel arch surface are deduced. And the forward and inversion method for the random receiving point and seismic focus point on tunnel arch surface is obtained based on the principles of wavefront diffusion and TRT inversion technology. With this method, the inversion results comply with that of TRT software with no restriction by channel numbers, ensuring enough effective channels involving in inversion in the case of some bad channels.