The invention discloses an expandable high-melt-strength polypropylene resin and a preparation method thereof. The method comprises: reacting and extruding raw materials including polypropylene, ultrahigh molecular weight polyethylene, petroleum resin, hyperoxide, bis[gamma-(triethoxysilyl)propyl]tetrasulfide, zinc oxide, stearic acid and the like in a parallel double screw extruder to obtain high-melt-strength polypropylene; and mixing the high-melt-strength polypropylene with liquid paraffin and azodicarbonamide at a high speed to obtain the expandable high-melt-strength polypropylene resin. The method disclosed by the invention is simple, low in investment and environment-friendly, and the extrusion performance of the melt is high.