A method for forming a horizontal overhanging structure without vertical support in selective laser melting, comprising: sequentially forming an initial layer, a repair layer and a conventional layer, wherein initial layer is printed by scanning at a speed set lower than the conventional speed using a laser spot in a defocused state, so that the Plateau-Rayleigh instability effect occurs in each track, to form an initial layer with a specific texture structure; repair layer is printed on upper surface of the initial layer by scanning at a speed set higher than conventional speed in a continuous-wave laser output mode using a laser spot in a focused state, and completes the transition from transition process parameter to conventional process parameters within the set number of processing layers; and conventional layer is printed on upper surface of repair layer using conventional process parameters, to form a horizontal overhanging structure without vertical support.