The invention discloses a flame-retardant high-temperature-resistance polyamide composition and a preparation method thereof. The composition is characterized by being prepared from the following components in parts by weight: 40-70 parts of polyamide, 5-15 parts of polyester, 0-10 parts of an impact-resistant modifier, 15-60 parts of a filler, 5-200 parts of a fire retardant and 0.2-1 part of a thermal stabilizing agent. According to the method, polyester and polyamide are mixed and modified, the polyamide carbonizing capability can be improved by means of polyester, the flame retarding performance of polyamide can be improved, the usage amount of flame retardant can be reduced, and further the attenuation of high-temperature aging resistance caused by introducing massive flame retardant can be further reduced; the alloy fluidity is further improved by using polyester, and the mold filling capability in the material injection-molding process can be improved. The flame-retardant high-temperature-resistance polyamide composition is especially applicable to the most advanced fields of precise electronic appliance parts, automobile engine compartment high-temperature high-humidity application environment, aerospace and the like.