Abstract: Using the WDJD-3 multi-functional digital DC instrument produced by Chongqing Bunting Digital Control Technical Institute, we design the observing system of cross-hole resistivity tomography to detect boulders in the laboratory, and take series of physical simulation experiments. Many arrays(cross-hole pole-pole, pole-bipole and bipole-bipole) are used in physical simulation experiments. The collected data is inversed by RES2DINV software and we get the following conclusions:(1) imaging results of pole-pole can't reflect the position and size of high resistance body; (2) both imaging results of pole-dipole and dipole-dipole in standalone mode can clearly reflect the position and size of the high resistance body. The results of physical simulation experiments indicate that cross-hole resistivity tomography can be used to detect high-impedance body. The survey method is flexible acquisition, obtaining stable and reliable data, setting clear visual image maps. The result of physical simulation experiment has a positive significance in detecting boulders in the hole of subway tunnel with cross-hole resistivity tomography. Three-dimensional resistivity tomography experiment in detecting boulder is in further studying.