Abstract: Research on height variation of plumes, which were formed by near free-surface underwater explosion of small TNT equivalent, has been done. With 0.6g RDX cylindrical charge, underwater explosion experiments were carried out at 14 detonation depth. Using two synchronous high speed video cameras, the water movement and bubble images were recorded and the height variations of plumes versus explosion depth and rising time were achieved through further data processing. By dimensionless treatment and polynomial fitting method, the engineering calculation model of the dimensional height was obtained. Comparing the calculated results with experimental ones for charge RDX of 1kg weight, the error was less than 5%. Research results show that the obtained engineering calculation model of the dimensionless plume is more versatile than Swisdak calculation formula. It is suitable for the height engineer calculation of near free-surface underwater explosion with small equivalent charge.