The invention discloses compound phosphorus-nitrogen series flame-retardant polyamide and a preparation method thereof. According to key points of the technical scheme, the compound phosphorus-nitrogen series flame-retardant polyamide is composed of the following components in parts by weight: 60.2-80.1 parts of PA resin, 0.1-0.3 part of liquid oil, 5-15 parts of melamine cyanurate, 5-15 parts of a phosphorus-nitrogen series flame retardant A, 1-3 parts of a phosphorus-nitrogen series flame retardant B, 2-4 parts of a phosphorus-nitrogen series flame retardant C, 0.3-1 part of metal chloride, 0.2-0.5 part of an antioxidant and 0.5-1 part of a lubricating agent. According to the compound phosphorus-nitrogen series flame-retardant polyamide disclosed by the invention, the ignition temperature of glowing filaments of the MCA system is improved, so that the temperature is higher than 750 DEG C, and the flame-retardant effect is greatly improved.