This paper presents a scheme using the DFT orthogonalizing pre-process to implement a wideband constant beamwidth pattern for the digital beam-forming antenna array.This pre-process decomposes the input wideband signals into orthogonal outputs at discrete frequency points in a relevant frequency band.The complex weighting vector at the reference frequency is evaluated using Genetic Algorithm to make the array reponse cater for the pattern specified. The complex weighting vectors at other frequencies satisfying the request of wideband constant beamwidth can be deduced from the one at the reference frequency.The results of computer simulation show this scheme is effective.