To circumvent the shortcoming of necessary conditions of optimality(NCO) tracking, namely that the optimizing period is relatively long, an explicit optimizing control approach based on output feedback is proposed. A number of off-line optimizations are carried out under various operating conditions, and the explicit model between optimal input and output variables is numerically established via function fitting. The model is used for online implementation and thus online gradient estimation is avoided. A continuous stirred tank reactor(CSTR) case is studied to demonstrate the advantages of proposed approach.