The invention relates to the field of organic high polymer materials, and provides a non-combustible high-temperature-resistant joint sealant. The joint sealant is prepared from the following ingredients in parts by mass: 40-80 parts of melamine formaldehyde resin, 10-30 parts of polyester polyol, 5-15 parts of cross-linking agent, 10-30 parts of foaming agent, 2-8 parts of DMF (dimethylformamide), 0.3-3 parts of DMDEE (2,2-dimorpholinodiethylether), 3-20 parts of chlorinated paraffin, 30-70 parts of TDI (toluene diisocynate) and 50-90 parts of MDI (diphenyl-methane-diisocyanate). The joint sealant provided by the invention can be used for constant-temperature construction, has the advantages of no toxin or harm, convenience in construction, good temperature resistance and cold resistance, no burning, no petroleum resin, good variability during vertical surface construction, no flowing, high cohesiveness, high elasticity, excellent waterproof performance, safety and reliability. A new product with reliable quality and high safe performance is provided for all walks of life which use the joint sealant.