The invention discloses fire-resistant flame-retardant composite thermal insulation mortar which is characterized by comprising the following raw materials in parts by weight: 300 to 350 parts of cement, 40 to 45 parts of clay powder, 23 to 26 parts of quartz powder, 12 to 15 parts of hydroxy propyl methyl cellulose ether, 40 to 45 parts of polypropylene short fiber, 30 to 35 parts of building crushed brick powder, 8 to 10 parts of antimony trioxide, 5 to 6 parts of sodium metasilicate, 4 to 5 parts of bentonite powder, 40 to 45 parts of oxidized starch, 24 to 28 parts of calcium propionate, 10 to 12 parts of borax, 30 to 35 parts of expanded pearlite powder, 5 to 10 parts of silica sol, 4 to 6 parts of modified nano-carbon powder, and 600 to 650 parts of water. The fire-resistant flame-retardant composite thermal insulation mortar mainly has the advantages that the workability, water-retaining property and heat insulating efficiency can be improved; common problems such as flaking, cracking and the like are solved; the anti-freezing, water-reducing, impermeable, durable, anti-crack, heat-insulating and heat-proof functions are realized after hardening.