A new method based cross-correlation technique (CD-OCT) is proposed to acquire and analyse the information about flow velocity with low signal-to-noise ratio(SNR) in spectral-domain optical coherence tomography(SD-OCT). We theoretically study the procedure of this method, and analyse the correlation between the noises by computer simulation and experiment. The Doppler flow images reconstructed by CD-OCT are compared with those reconstructed by Joint spectral and time-domain optical coherence tomography (STD-OCT). The results demonstrate that CD-OCT can significantly improve the SNR, thus rendering it suitable for the flow measurement in low SNR.