The invention discloses a long-carbon-chain polyamide and polyether block copolymer with low water absorption rate and high polyether content, and a preparation method thereof. The long-carbon-chain polyamide and polyether block copolymer is mainly prepared by copolymerizing a polyamide block and a polyether block, the polyamide block accounts for 10 to 60 percent of the total weight of the copolymer and the polyether block accounts for 40 to 90 percent of the total weight of the copolymer; the polyamide block is a fatty polyamide copolymer, and is obtained by neutralizing fatty straight-chaindiamine and fatty straight-chain dicarboxylic acid till salifying and performing melt polycondensation; and a polyamide block prepolymer, polyether polyol and a catalyst are put into a high-pressurereaction kettle and are subjected to reaction at specific temperature and under specific pressure to perform block copolymerization to form the polyamide and polyether block copolymer. The copolymer has lower water absorption rate, high processing flowability, higher size stability, tensile resistance, toughness and softness, and the water absorption rate is 0.2 to 1.5 percent.