An efficient combined maximum likelihood (ML) and decision feedback equalization (DFE) decoding method is proposed for a coded double space-time block code orthogonal frequency division multiplexing (DSTBC-OFDM) system. For the missing bit log likelihood ratios (LLRs) in the DFE part, our proposed detector effectively exploits Gaussian approximated LLRs with reference to the colored noise covariance matrix. Simulation results demonstrate that the proposed method can achieve comparable performance to the coded full ML detectors with deterministic and lower complexity.