This paper considers an optimal control problem of chemical processes with a small perturbation in the system state and control input inequality constraints. Since open loop controls may not be robust in practice engineering applications, a general state-feedback controller is introduced for the biochemical process optimal control problem. Then, in order to obtain the optimal state-feedback parameters, a numerical optimization algorithm is proposed for solving this problem based on a novel smoothing cost penalty function approach. Compared with the existing methods, this algorithm has two advantages. One is the penalty parameter need not take a very big value or go to infinity. The other is guaranteed to converge to a local optimal solution without the requirement of the global solution being obtained at each step. More importantly, an effective sensitivity analysis method is also developed for the chemical process optimal control problem. Finally, three chemical process optimal control problems are provided to illustrate the effectiveness of the proposed method. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.