The invention discloses a steam distributing method and device of a steam turbine set. The method comprises the following steps: acquiring design parameters of the steam turbine set and the set running data; building a steam flowing field model based on the design parameters and the set running data; determining a target valve sequence combination of the steam turbine set based on the steam flowing field model; and controlling high-pressure adjusting door opening sequence of the steam turbine set based on the target valve sequence combination. According to the method, an original steam distribution mode of the set remains; a set of scientific and complete method is provided; a set of steam distributing control scheme for realizing economic operation is re-designed and added; an original complex steam distributing mode is carried out in set start-stop and low-load stages; sequential valve steam distributing adjusting is carried out after certain load is applied; the two modes can be flexibly switched online, so that the operation economy of the set in high, intermediate and low loads can be improved; and the technical problem of low operation economy of an existing complex steam distributing method under intermediate and low loads can be solved.