The invention discloses a method for solving transverse cracks of an ultra-thick plate billet corner by applying a 3D (Three-dimensional) spraying process, belonging to the technical field of steelmaking continuous casting secondary cooling system. The method comprises the following process steps of: determining fan-shaped sections for installing 3D nozzles; determining a distribution principle of the position of each 3D nozzle at each fan-shaped section; determining the distribution mode of the 3D nozzle at each fan-shaped section along a billet drawing direction; and determining the distance between a spraying edge of the 3D nozzle at each fan-shaped section and a cast billet corner part. The method has the advantages of controlling the incidence rate of the transverse cracks of the ultra-thick plate billet corner effectively, and improving the molding rate of the steel billet.