The process of air separation unit has the characteristics of many types of equipment, long flow, and strong relativity and complicates structures. A multi-variable model predictive control strategy to achieve the goal of automatic variable-load for the control limits in the variable-load process of air separation unit was proposed. Regard model predictive controller as the core, the problems of coupling in the various technological parameters were solved. Moreover, the non-linear control request for global variable-loading process was satisfied, and the perfect operation character and rate were ensured. Production characteristics, structure, scheme and application processes for the control strategy were described in detail. The system succeeds in applying to the air separation unit in an iron and steel enterprise, the multi-variable control system shows its effectiveness and efficiency in the automatic variable-loading.