The invention provides a construction method for full-casing long spiral bored piles. The method includes the steps that firstly, a casing pipe and a spiral drill pipe of a full-casing long spiral drilling machine simultaneously rotate and sink so as to form a hole after being aligned with a pile position; secondly, the drilling machine is moved to the next pile for hole formation operation, and meanwhile, adhering soil on the inner wall of the casing pipes in the formed hole is removed in a brushing mode through a wall brushing device; thirdly, a reinforcement cage is hoisted into the hole, concrete is poured into the reinforcement cage, and concrete pouring is stopped after the concrete is poured to the top elevation of the reinforcement cage; fourthly, a cage pressing device is hoisted into the casing pipe, and concrete pouring continues; fifthly, a pile machine is located in place, and a drill bit is elevated to the cage pressing device to press the reinforcement cage; and finally, the casing pipe is lifted and pulled out, the cage pressing device is removed, and pile forming is completed. The construction method provided by the invention is high in construction efficiency, the wall of a formed pile hole is regular in shape, a pile body is high in perpendicularity, and the pile forming quality is good; soil squeezing, hole collapse and vibration are avoided, and construction noise is low; and slurry pollution in the construction process is avoided, the outward slurry transport cost is reduced, the cost is reduced, and the construction method is environmentally friendly.