The invention discloses an automatic polypropylene random (PPR) pipe assembly hot-melt welding device which comprises a base, wherein a portal frame is arranged above the middle of the base; a hot melt machine is arranged on a beam; a hot-melt die head is arranged below the hot melt machine; pipe transfer mechanisms are symmetrically arranged on the front and rear sides of the portal frame; the pipe transfer mechanisms comprise sliding seats capable of moving back and forth; two groups of pipe assembly clamping mechanisms are arranged on the left and right sides of the sliding seats in parallel; down pressing pipe mechanisms are arranged on the sliding seats between the two groups of pipe assembly clamping mechanisms; the pipe assembly clamping mechanisms comprise positioning blocks and telescopic cylinders; the positioning blocks are arranged at one ends, which are close to the portal frame, of the sliding seats; the telescopic cylinders are arranged at one ends, which are far away from the portal frame, of the sliding seats; piston rods of the telescopic cylinders are connected with top pipe columns of the positioning blocks. The invention has the beneficial effects that the hot-melting and fitting operations of the pipe assemblies can be mechanically completed, the hot-melting effect is good, the fitting is accurate, high sealing property is guaranteed, the manual labor is saved, and the working efficiency is greatly improved.