A retaining joint for fixing a cable includes a joint unit having a hollow body; the hollow body having a resisting ring; a front side and a rear side of the resisting ring having a first combining portion and a second combining portion, respectively; the first combining portion serving for combining with a locking unit; a front end of another second combining portion being connected to a plurality of clamping sheets; a tightening element having a through hole; an inner surface of the tightening element having a thread for combining with the second combining portion; an inner wall of the tightening element being protruded as an extrusion surface for clamping and compress the clamping sheets to clamp the protection tube; and a protection tube being a hollow body; a surface of the protection tube being formed with a plurality of protruding rings and a plurality of recesses.