During the past few years, single-carrier modulation (SCM) has again become an interesting and complementary alternative to OFDM system because of the implementations of frequency-domain equalization (FDE) with FFT/IFFT. The performance of SC-FDE system suffers severely by the time- and frequency-selective fading, hence, powerful forward error protect coding and modulation scheme are essential to the system. In this paper, we proposed a multilevel coding-modulation scheme based on convolutional codes and 16-QAM modulation for SC-FDE systems. The corresponding multistage decoding (MSD) algorithm is developed in this paper; system performance tests over AWGN and fading channel based on simulation indicate that the SNR requirement is more than 1,5dB lower than that of a single level coded system when BER is 10^-7