The invention discloses a turning method of a long thin wall composite shell body formed by metal and glass fiber reinforced plastics. The method comprises the steps that (1) glass fiber reinforced plastics outer circle rough turning is carried out; (2) the two end faces of the shell body are subjected to rough turning; (3) glass fiber reinforced plastics outer circle fine turning is carried out; and (4) the two end faces of the shell body, an inner hole and an annular groove are subjected to fine turning. Rough-fine machining processes are used, technology allowance is distributed reasonably, deforming amount is controlled, metal shell inner hole accuracy is controlled and is used as the machining standard of a structure piece after recombination, an end cap and a soft claw are used for clamping, clamping deforming is lowered, through a low-temperature cold air cooling mode, a cutting environment is improved, a tool and cutting parameters during cutting machining are stipulated, product tool service life is prolonged, and machining efficiency is improved. The technology method is reasonable and reliable, product deforming is small, and the machining quality of the composite shell body can be effectively guaranteed.