The invention belongs to the technical field of coal mine machines and relates to a soft starting device, in particular to an open type valve-control liquid filling type liquid coupler. The open type valve-control liquid filling type liquid coupler aims at overcoming the defects in an existing transmission technology according to operation characteristics of a high-power scraper conveyer in an underground coal mine. The open type valve-control liquid filling type liquid coupler is mainly composed of a main frame, a sub-frame, pump wheels, worm wheels, a transmission shaft, centrifugal valves, a liquid filling solenoid valve, a rotation speed sensor, a temperature sensor and the like. According to the open type valve-control liquid filling type liquid coupler, a double-pump-wheel structure and a double-worm-wheel structure are adopted to increase the moment transmission capacity, a centrifugal valve structure is designed to adjust the liquid filling rate of a working cavity, and the transmission shaft is connected with a worm wheel connecting sleeve in a keyless interference mode, so that torque is ensured, the installation space is reduced, and the open type valve-control liquid filling type liquid coupler integrally has good self-cooling, soft starting, overload protection and power balance performance, is easy and convenient to operate and maintain and provides a reliable guarantee for efficient and stable operating of the coal mine high-power scraper conveyer.