Abstract: High Range Resolution (HRR) Radar extends the target into multiple scatterers, hence improve the signal to clutter ratio (SCR), which makes it in favor of marine target detection. However, with this technique the probability distribution function (PDF) of the collected echoes has a long tail, i.e. it is non-Gaussian, which will lead to performance deterioration of classical constant false alarm rate (CFAR) detectors. Improvements can only be made with a deep understanding of the characteristics of the sea clutter. In this paper, the characteristics of sea clutter amplitude distribution, power spectrum and time and space correlation are analyzed with field data. The performances of traditional CA CFAR and OS CFAR are analyzed and compared. Finally, an engineering improvement of sub-frame integration was proposed. With an acceptable deterioration of detection probability, the method can well reduce the false alarms in target tracking.