As Oliveira et al. (2014) summarised, based on time-series synthetic aperture radar (SAR) data, potential uses of persistent scatterer interferometric SAR (PS-InSAR) technique include (i) the identification of individual landslides and the delineation of generalized unstable areas; (ii) the redefinition of limits of ancient landslides; (iii) the identification of landslides based on the multi-temporal comparison of SAR images in specific event; and (iv) the automatic slow-moving landslide mapping based on the application of a spatial statistical approach. Although the number of successful PS-InSAR applications covering topics summarised above is increasing, there is an issue still remained unclear - that is the optimal strategy for extracting reliable PS through interferometric SAR analysis. For which this is highly relevant with the phase coherence threshold value applied in PS-InSAR processing. Normally lower coherence value results in larger number of PS points, however their reliability is uncertain. In order to understand the physical characteristics of the PS points extracted using different phase coherence threshold, we choose sites with various land cover types in northern Taiwan as the study area. SAR data of different wavelengths and the GIAnT software allowing SBAS, N-SBAS, TimeFun and MInTS are employed in the experiments. Once the PS-InSAR processing is finished, ortho-rectified aerial photos or spaceborne optical images are used to check the ground truth/terrain features on corresponding location of extracted PS points. In addition, ground surveying data including levelling and GPS observation are used to examine the accuracy of the computed displacement of PS points. Combined with the physical characteristics and geometric accuracy, the reliability of the PS points can be determined. Meanwhile the optimal phase coherence can be revealed.