Abstract: (Objective) The geophysical method can effectively monitor the dynamics of water flow and material transport in 4-D hydrogeological processes, and its imaging accuracy is often closely related to the monitoring scheme. Taking the commonly used Electrical resistivity tomography (ERT) as an example, in order to obtain good imaging accuracy, a large number of electrode arrangements are often required, which leads to a long monitoring time and therefore cannot timely respond to the 4-D hydrogeological dynamic process. Most of the existing ERT monitoring scheme optimization studies focus on surface ERT, and few focus on cross-hole ERT. (Methods) Since cross-hole ERT has more advantages in the high-precision characterization of the study area, this study proposed to optimize the monitoring scheme of cross-hole ERT by Bayesian experimental design. By comparing the measurement time and accuracy of the optimized electrode arrangement with the traditional electrode arrangement through indoor static/dynamic tests and field sites, the validity of the optimization scheme of Bayesian experimental design was verified. (Results) The laboratory test results showed that the optimized monitoring scheme could reduce the measurement time by about 75%, and the inversion results of the optimized scheme could more accurately depict the dynamic resistance anomaly region, significantly improving the hysteresis error of the traditional scheme monitoring the 4-D hydrogeological process. Field test shows that the optimized scheme can reduce about 95% monitoring time under the premise of ensuring monitoring accuracy. (Conclusion) Optimizing the monitoring scheme of cross-hole ERT electrode arrangement based on Bayes experiment design provides technical support for efficient monitoring of 4-D hydrogeological processes.