A modern air separation plant control system must solve a host of problems, including variation in conditions of plant operation with full guarantee of its automatic flow. The procedure of gearing the plant from one operation mode to another is based on gradual change of control action and collection of desired products without impairment of their quality below the allowable level. To accomplish this task, it is essential to determine the values of the key process parameters for various air separation plant operation conditions and the maximally allowable control action variation rate. Based on the investigation results and comparative analysis of the values of the key process parameters of optimized static-state regimes in UniSim Design environment and actual indicators with a real plant, we found insignificant deviation of the calculated parameters from the actual values during the plant operation. It was concluded that the results of air separation process modeling in UniSim Design environment or the magnitudes of control actions derived by equations of material and heat balances of the plant can be used, in a first approximation, in plant operation mode change algorithm.