The invention discloses a flame retarding polypropylene resin blend and a preparation method thereof. The flame retarding polypropylene resin blend is prepared according to a weight ratio by 56-90 percent of polypropylene resin, 3-18 percent of flame retardant, 3-6 percent of auxiliary flame retardant, 1-6 percent of flame retarding synergist, 2-8 percent of compatibilizer, 0.5-5 percent of melt strength regulator, 0.1-0.5 percent of antioxidant, 0.1-0.5 percent of heat stabilizer, and 0.3-0.5 percent of light stabilizer. The components are mixed in a high-speed mixer for 2-5 minutes, then extruded by a twin-screw extruder and finally granulated. The flame retarding polypropylene resin blend of the invention can maintain a flame retarding property, and at the same time, has the advantagesof low proportion, excellent mechanical property, long thermo oxidative aging, excellent lightfast aging capability, and reduced flame retardant migrating, etc.