This study proposes a tomography-based method for evaluating grouting performance after injection. Tomography is a convenient approach for solving the boundary measurement inverse problem of capturing discrete pixels and synthesizing these pixels into a unified image. Four arrays of eight electrodes are installed into large triaxial cell specimens to simulate in-situ crosshole resistivity testing. Sand is used as a base material and a wet cement mixture is grouted into the specimens. Electromagnetic waves are used as a means of accumulating the physical properties of the specimens. Each measured electrical resistivity is considered as a discrete signal. The electrical resistivity distribution is calculated and optimized through an iterative modified least-squares inversion based on a forward solution of Coulomb and Gauss's law equations. Results show that the electrical properties of an injected grout material and its location and size can be effectively estimated from a series of resistance measurements.