The invention discloses a reducing parallel groove clamp, which comprises upper clamp bases, a lower clamp base and fastening bolts, wherein the lower clamp base is provided with at least one upper clamp base; a lower large-diameter groove and a lower small-diameter groove which are symmetrically arranged in parallel are formed in the lower clamp base; the radius of the lower large-diameter groove is greater than that of the lower small-diameter groove; an upper large-diameter groove and an upper small-diameter groove are formed in each upper clamp base; the upper large-diameter grooves are located above the lower large-diameter groove; the upper small-diameter grooves are located above the lower small-diameter groove; grooves which are equal to the upper clamp bases in quantity are formed in the bottom surface of the lower clamp base; a lower through hole is formed in the center of the bottom surface of each groove; and an upper through hole is formed in each upper clamp base. The reducing parallel groove clamp has the advantages that a cable can be conveniently clamped into the corresponding groove; and the reducing parallel groove clamp can be directly used when two cables with different diameters need to be connected, so that complete contact of the upper clamp bases and the lower clamp base and the cables is ensured; the pole-mounted operation time is shortened; and the unified construction technology is ensured. Meanwhile, the grooves are formed in the bottom surface of the lower clamp base, so that the contact area with the fastening bolts or nuts can be expanded; and the clamping force of the upper clamp bases and the lower clamp base is ensured.