According to the requirements of field control of dye ingredient, an automatic control system of dye formulation based on Siemens PLC and Metler-Toledo weighing instrument is designed. The upper computer running system is completed by Kingview 7.5 configuration software. The whole system realizes high precision automatic control of dye formulation. It has the characteristics of reliable communication and simple operation. It effectively improves the production efficiency and guarantees the stability of the system.