The invention relates to a y-shaped branched chain external fixator for long bone deformity correction, the external fixator comprises a near-end ring, a far-end ring, a y-shaped composite branched chain and a spin adjusting assembly, the y-shaped composite branched chain is composed of a long branched chain and a short branched chain, and the short branched chain is connected with the top of a lead screw sleeve of the long branched chain through a hooke joint rotating base; the self-rotating adjusting assembly is arranged at the bottom of the far-end ring of the external fixator, so that an independent self-rotating degree of freedom is increased, and when rotational deformity needs to be corrected, the self-rotating adjusting assembly is adjusted firstly to correct the rotational deformity, and then deformity in other directions is corrected. By arranging the y-shaped branch chains and the self-rotation adjusting assembly, the capacity of correcting rotation deformity of the externalfixator is improved, interference and collision between the branch chains and between the branch chains and limbs during deformity correction are avoided, meanwhile, space 6-DOF movement can be achieved, and three-dimensional bone deformity in any space can be corrected.