A cable connecting assembly includes a tubular member, a securing member, a seal unit, and a hollow barrel member that defines an accommodating space. The tubular member is disposed in the accommodating space and has two annular grooves. The securing member has a coupling portion abutting against the tubular member and threadedly engaging the barrel member, and an abutment portion abutting against the barrel member. The seal unit includes two first seal rings respectively disposed in the annular grooves and sealingly contacting an inner surface of the barrel member, and a second seal ring sleeved on the coupling portion of the securing member and sealingly contacting the inner surface of the barrel member and the abutment portion of the securing member.