In order to improve the stability of the multi-hydro-turbine governing system with sharing one penstock (MGSSP) during operation, an intelligent CPSOGSA-based mixed H2/H∞ robust controller with an integrator is proposed. The excellent control performance of the H2/H∞ robust controller is used to stabilize the system. Firstly, the mathematical model of the MGSSP is derived from the transfer function. Secondly, the robust controller is designed based on the linear matrix inequality (LMI), considered the optimal and robust performance. The modified hybrid PSOGSA with chaotic maps algorithm (CPSOGSA) is also introduced in the design process to ensure the controller is optimal. The designed robust controller is simple in structure, low in order, and easy to implement. Simulation experiments show that the CPSOGSA can complete the optimization of the controller with less than ten iterations. The designed robust controller can stabilize the system in less than 10 s for different operating conditions. The robust controller enables the controlled object to exhibit better dynamic performance than the conventional controller. The research results can provide a reference for the control application of the extended operation of the hydro-turbine governing system (HTGS).