The present invention relates to heat melting butt jointing welder for plastic pipe and belongs to the field of plastic pipe welding apparatus making technology. The heat melting butt jointing welder includes mainly frame comprising upper frame with controller, lower frame, etc.; clamping mechanism comprising fixed clamps, movable clamps, etc.; cutting mechanism comprising sliding track with turning cylinder, sliding seat with translation cylinder, cutting motor with reducing box, cutting board with lathe tool, etc.; and heating mechanism comprising upper sliding seat, lower sliding seat, heating board sliding body, heating board holder with heating board, etc. The present invention has reasonable design and compact integral structure, and may be used in completing clamping, cutting, heating and butt jointing of different kinds of plastic pipes, especially plastic pipes of caliber as great as 800-2000 mm.