Description:   In this paper,we first review the time-frequency analysis and time -frequency-based detection methods.Secondly,by analyzing a mass of the measured data of sea clutter,we show the difference of time-frequency geometric features between echoes with a target and pure sea clutter.Finally,we given the detection algorithm based on the time-frequency geometric features.The results of the measured data show that the proposed method can effectively find low-velocity small targets in sea clutter.This approach is a novel try to detect small targets in sea clutter.