The invention relates to a converter station and a converter station and submodule voltage equalization control method in the switching-on and switching-off process of a single valve group of the converter station, the converter station comprises two MMC valve groups connected in series, a single valve group at least comprises a half-bridge sub-module and/or two clamping sub-modules, the valve group is put into the circulating current controller during the valve group input/output process, the output of the circulating current controller is superposed on the corresponding phase, and the lowerbridge arm modulating wave is used for triggering control of the corresponding bridge arm sub-module; the circulating current controller is used for making difference between the circulating current command value and the phase-to-phase circulating current value detected in real time, and regulating the circulating current controller to obtain an output quantity after regulating by a regulator. Theinvention can artificially create positive and negative alternating bridge arm currents to avoid overvoltage or undervoltage phenomenon of half-bridge sub-modules and/or clamping twin sub-modules when the bridge arm currents are continuously positive or negative in the process of single valve group switching-on and switching-off process; and moreover, the invention only aims at the improvement ofthe control strategy, does not need to increase the number of the full-bridge sub-modules, reduces the equipment cost, and has strong practicability.