The invention provides a nozzle arrangement method and system for a billet caster and a slab caster. The method includes the steps that arrangement parameters of all nozzles of a second cooling section are set preliminarily; a local Cartesian coordinate system of each nozzle is established; casting blanks are simulated through the grid technology; the radiation vector of each spatial water dipping point is determined by using each grid center point as the spatial water dipping point; the Euler angle of the radiation vector of each spatial water dipping point in a caster coordinate system relative to the normal direction of the grid where the spatial water dipping point is located is determined; according to the water amount distribution and radiation vector of each spatial water dipping point of the nozzles, the angle density of the spatial water dipping point can be determined; in accordance with the angle density, the radiation vector and the Euler angle of each spatial water dipping point, the water flow surface density of the grid where the spatial water dipping point is located can be determined; according to the water flow surface density of the grid where each spatial water dipping point is located, a casting blank surface temperature variation curve can be obtained; and based on the casting blank surface temperature variation curve, the arrangement parameters of all the nozzles can be adjusted according to the trend that the longitudinal and transverse temperature distribution on the casting blank surfaces is uniform.