The utility model provides a valve rod length detector which the characteristics are the left part side of the being equipped with body groove seats on the platform of bottom surface, and it has vertical V type recess to open on the right flank of square body groove seat, is equipped with the transverse strut who puts on the right side on the seat of V type recess front side side body groove, and transverse strut's right -hand member is equipped with rearmounted vertical die -pin, and compression screw is equipped with to the rear end of vertical die -pin, and compression screw's axis is crossing and perpendicular with the axis of V type recess, the rear side of V type recess is equipped with the tongue. It has solved artifically with slide caliper rule or the coarse problem of depth gauge rule measurement valve and valve rod, is particularly suitable for valve manufacturing enterprise and uses.