To use the Automatic identification system (AIS) as a land-based positioning system for coastal vessels is a leadingedge research field. The timestamp detection method used in the AIS is quite different from the one used in general positioning system. We researches the transmission model of AIS signal over sea surface. The influence of different sea surface conditions on the propagation losses of AIS signal was analyzed. Based on the relationships between different meteorological conditions and the propagation losses, the relationship between the propagation losses and the performance of timestamp detection, an adaptive method is proposed to be used in the AIS real-time signal detection. The proposed method can adaptively determine whether to conduct the noise resistance procedure or not according to the sea surface conditions. The experimental results indicate that the timestamps can be detected precisely while the processing time is reduced about 67%. The proposed method is valid under different conditions and achieves a good performance in the field test.