The invention discloses a flame-retardant thermoplastic composite and a preparation method thereof, the flame-retardant thermoplastic composite comprises the following components according to parts by weight: 40-80 nylon resin, 3-36 red phosphorus flame retardant, 1-50 filler, 0.01-3 phosphorus precipitation stabilizer and 0-50 other additives; and the phosphorus precipitation stabilizer is one or more than two of copper complexes and copper halides. The flame-retardant thermoplastic composite can greatly reduce the precipitation amount of phosphorus, improve the stability and lead a materialto have good flame retardance and mechanical strength; and a molded product with low wall thickness has UL94 classified as V-0 or V-1, improved phosphorus precipitation stability. The flame-retardantthermoplastic composite is applicable to sheets, plates and the molded products, in particular to electrical appliances and electronic parts, the specific applications are lamps, such as lamp holder,plug, permeator, coil rack, capacitor box body or connector, circuit breaker, housing of relay, reflector and the like.