The mechanism of hydrogen chloride synthesis is analyzed, and the main factors affecting the ratio of chlorine and hydrogen in hydrogen chloride synthesis are found out. For hydrogen chloride synthesis procedure which is nonlinearly coupling, lagged, multivariate and multiple correlation control object, a chain system control method is brought forward to control the ratio of chlorine and hydrogen in hydrogen chloride synthesis process. The cause and effect relationships of key factors are analyzed, then build the model which consisted of four unit models and two causality chains. Through the field data simulation, the results show that the chain system model has strong real-time performance, stability, anti-interference ability, and the control effect is good.