Though the power line's diameter was only 1~3 centimetres, it could generate strong reflection in high resolution strip mode SAR images while the line direction was along the radar azimuth. This paper chose one set of line scatterers and analysed the changes among time series images in HK area. There were 8 line scatterers in these set which reflected by 6 power wires and 2 ground wires. Each of the line scatterers' magnitude, area and position had been analysed during data acquiring period. In time series SAR images, the maximum magnitude of the power line scatterers, the scattering area above 50db and the central position of the scatterers changed in various trend. Adaptive window maximum coherence algorithm has been applied to extract the reflection position. This paper showed how the power line sag changed and reflection position changed in time series images. It seemed that the temperature should be the main factor that changed the sag position and changed the reflection geometry.