Unique multi-channel flow path is designed and peristaltic pumps are used. Supplemented by automatic control system, the digestion, color, measurement and data processing are separately completed and the total phosphorus and total nitrogen of seawater are automatically measured. The detection limits are 0.00174mg/L (TP) and 0.00375mg/L (TN). The relative standard deviations are 7.06% (TP) and 2.17% (TN).The detection extraction recoveries are 98.1% (TP) and 92%(TN).