The invention provides a practical on-line forewarning method for the production process of synthesizing vinyl chloride through an acetylene method. A data driving and monitoring model is built through data such as the gas-phase feeding temperature and flow of acetylene and vinyl chloride and the mixer temperature in the real process under the normal operation condition. On the basis, the characteristics of different types of faults are studied and analyzed, and a reasonable alarming strategy is designed according to the characteristics.