Abstract: Based on the precise design theory of steel manufacturing processes, a two-step design method using Gantt chart combination was proposed.Firstly, the initial steel production process was established by the traditional design method according to the product mix.Secondly, the combination modes of Gantt chart equations were established based on the reasonable Gantt chart combination modes and the yield proportion of each steel grade in the product mix.The equations were solved by the successive over-relaxation iteration method to calculate the process productivity.The result shows that the process productivity is less than the productivity of equipment in the traditional design method.By the productivity calculation method based on Gantt chart combination, the influence law of the nominal capacity of decarbonization converters and casting speed on the process productivity and the operation rate of equipment was analyzed, and the rational process productivity and casting speed were proposed according to different nominal capacities of decarbonization converters.