Under adverse sea conditions such as long period waves and few construction period,the traditional multi-beam monitoring technology has low precision,only ±10cm.Relying on the Ashdod port project in Israel,we analyze the various error sources with and without tide testing based on the common format data of multi-beam,compare a variety of filtering algorithms,and develop the multi-beam high-precision automatic post-processing software.The results show that the software can achieve quasi real-time monitoring of the riprap state of the slope under adverse sea conditions with an precision of ±5 cm.