Deformation monitoring is essential to the safe operation of seawalls. This paper reports the Interferometric Synthetic Aperture Radar（ InSAR） measurement results derived from 31 Envisat ASAR images acquired over Hang zhou from 2006 to 2010

with special focus on the seawall in the Qiantang Estuary. Multi-temporal InSAR（ MTInSAR） was used to extract deformation information from both Persistent Scatterers（ PSs） and Distributed Scatterers（ DSs）

which provide dense measurement of the deformation of the seawall. Compared with the leveling measurement at 28 points

the mean error derived by InSAR is 0. 436 mm

with the largest error of 5. 016 mm

which confirms the millimeter-level precision and accuracy of the InSAR technique. A time series analysis was conducted based on these two datasets

and results showed that the subsidence of seawalls was spatially continuous and had a local negative unimodal pattern with distance. A linear tendency with minor local fluctuation was also observed in the time domain during a period of nearly seven years.