Abstract: The experiments of underwater ventilated projectile were conducted to investigate the ventilated supercavity. The ventilated supercavity was formed by means of ventilating the underwater projectile, and then the shape of the supercavity was investigated. Under the condition with different cavitation number, the ventilation coefficient was obtained. The experimental results show that, when the cavitation number is large, the ventilated supercavity is mainly caused by small ventilation coefficient, while when the cavitation number is small, the ventilated supercavity is cause by large ventilation coefficient. The drag reduction characteristic of the ventilated supercavity was validated, and the velocity and displacement of the ventilated and non-ventilated projectile with the same initial velocity were compared. The results show that, when the ventilated supercavity forms, the attenuation of the velocity becomes slow and the displacement is large. On the other hand, the non-ventilated projectile forms partial cavity, as a result, the attenuation of the velocity becomes fast, and the displacement is small.