Abstract: In order to study ultrasonic through-transmission testing technique based on water-squirting coupling for aerospace composites, a water-squirting ultrasonic testing system is developed, with specific nozzle and two probes being designed and applied in the system. Based on this system, the water-squirting parameters, such as squirting speed, squirting distance and squirting angel are experimentally studied, and the affecting regulations are obtained. Experiments show that technical parameters greatly affect testing results, and their reasonable ranges of choice are given. The conclusions are of great significance for design of automatic water-squirting ultrasonic testing system and optimization of the testing technical parameters.