The invention relates to an industrial unit dichloroethane cracking furnace coupled modeling method and application. In the method, during modeling, a dichloroethane cracking furnace is divided into a hearth model and a furnace tube model, a one-dimensional partition method in combination with method is used for the hearth, the smoke temperature distribution condition of the hearth is solved by a heat balance equation, for the furnace tube model, the furnace tube is partitioned according to the amount of straight tube sections of a radiant section, and the reaction and the heat absorption capacity in the tube are calculated section by section. The hearth model and the furnace tube model are mutually iterated through a quasi-newton method according to the calculated smoke temperature and heat transfer rate information, until meeting the convergence precision and the model precision. The model is based on the dynamical model and the energy conservation relation, and is corrected by real-time data so as to further measure the relevant parameters of the cracking furnace in a soft sensing manner. The accurate model is the basis of optimization, provides reliable model basis for optimization of field important economic indicators, such as the outlet temperature of the furnace tube of the cracking furnace, the dichloroethane cracking conversion rate, the selectivity, the unit consumption and so on, and realizes real-time soft sensing of relevant parameters.