The invention discloses a method for preparing gray high-flame-retardant polypropylene foaming beads. The method comprises the following steps of: (1) mixing, in parts by weight, 100 parts of polypropylene resin, 10-35 parts of compound flame retardant, 0.5-15 parts of gray masterbatches and 0.1-5 parts of a foaming assistant at a high speed so as to obtain modified polypropylene particles; (2) putting the modified polypropylene particles into a reaction kettle, then performing heating and pressurization, and releasing the reaction kettle to atmospheric pressure instantaneously to obtain the foaming polypropylene beads. According to the method for preparing the gray high-flame-retardant polypropylene foaming beads, a synergistic effect can be generated by carbon black and the compound flame retardant which is prepared from, by weight, 100 parts of polypropylene resin, 10-35 parts of magnesium hydroxide, 5-19 parts of aluminum hydroxide, 2-8 parts of ammonium polyphosphate and 5-10 parts of antimony trioxide, and carbon black and the compound flame retardant are balanced by each other, so that the test result of the oxygen index of the gray high-flame-retardant polypropylene foamingmaterial reaches up to about 37%, and meanwhile it is ensured that the EPP beads can be formed in a normal vapor range, and fusion can be achieved among the beads well.