The invention provides an ultrahigh pressure water jet impact power performance measuring system and method in coal dust mixed liquor flooding. The system mainly includes an ultrahigh pressure water pump, a pressure control device, a fluidic generator, a computer, a pressure collector and an experiment cavity, and also includes a pressure sensor, a target board, a guide rail and a stirrer disposedin a test cavity. By utilizing the system, the ultrahigh pressure water jet impact power performance in coal dust flooding can be measured, which has great theoretical and practical guiding significance to discovering optimization of an ultrahigh pressure water jet slotting technology. The system and method are high in practicability and can realize measurement of ultrahigh pressure water jet impact power performance in coal dust flooding in conditions with different target distances, jet impact angles, jet impact pressures, coal powder masses and particle sizes, and are convenient in operation and safe and reliable in use.