To investigate the capability of electrical resistivity tomography for characterizing heterogeneous karst conduits, laboratory model tests on the detection of heterogeneous karst aquifers were conducted under different boundary layouts and excitation source conditions. The experimental results indicate that compared to the observation mode with insulated boundaries, using controlled electrical potential boundary conditions as inversion constraints for electrical resistivity tomography detection can effectively reduce the uncertainty of estimated parameters. With the increase in the number of electrical potential boundaries, the characterization accuracy of electrical resistivity tomography for heterogeneous karst conduits gradually improves. Compared to the mode with constant current excitation sources, the mode with constant voltage excitation sources has higher imaging accuracy and inversion certainty, but the estimated conductivity is relatively high. The electrical resistivity tomography technique based on a successive linear estimation algorithm can effectively characterize the heterogeneous characteristics of the conductivity distribution in karst aquifers.