Abstract: Reduced-space SQP algorithms for optimization of distillation column are studied.Variables decomposition is used to eliminate dependent variables and equality constraints,which reduce the dimension of QP sub-problems involved in iterations of SQP.Compared with the one based on orthonormal bases,reduced-space SQP based on orthogonal bases retains the convergence property while avoids QR decompositon.The improved computation efficiency is illustrated in a enzene/toluene distillation column optimization example, based on authors,previous work.