The invention provides a design method of a swirl nozzle for round billet continuous casting, which relates to the technical field of metal casting. Firstly, the flow of molten steel in a three-dimensional mathematical model is simulated by modeling software Gambit and flow calculation software Ansys Fluent, and then the velocity and temperature fields of the cross-section and the longitudinal section of the slab below the nozzle in the mould are extracted. Finally, by analyzing the flow field and temperature field of different nozzle shapes, a more suitable shape of immersed nozzle for roundbillet is obtained. According to the design method of a swirl nozzle for round billet continuous casting, a more suitable swirl nozzle can be obtained, the molten steel form is made more durable and effective horizontal swirl motion in the working area of the mould, the dissipation of the overheat is promoted, the rise of the high temperature area in the mould is increased, part of the free crystal is made to remelt, the overheat is reduced, and enlargement of the equiaxed crystal area and improvement of the quality of the core of the mould are facilitated.