A totally implantable venous device includes a port, a catheter and a sleeving member. The port includes an arcuate housing having a recess on an inner surface, an opening communicating with the recess and having a flat mouth, an internal chamber, and a base formed of hard plastic and being capable of preventing a needle from being inserted therethrough. The catheter includes an enlarged fastening member at one end. The sleeve is complementarily mounted on a front portion of the enlarged fastening member. The sleeving member is complementarily mounted on the remaining portion of the enlarged fastening member. The recess and the opening form a through hole having an enlarged intermediate portion. The enlarged fastening member has a truncated trapezoidal shape. The sleeving member, the enlarged fastening member and a connector of a receiving seat in the port form a watertight structure at the through hole.