The source water salinity of Suizhong 36-1 oilfield was as high as 9548 mg/L, and the ion concentration of magnesium and calcium was of 819.94 mg/L. As a result, the problem of water injection line scaling was serious. The well scaling products were analyzed by ESEM, EDS and XRD. The results showed that the calcium carbonate scales which in the surface pipeline and the underground string were significantly different in crystal feature, granularity and shape. The scale produced from underground string was calcite, which had complete crystal shape and coarse grains. The main elements of scale products included O, Si, Ca, C and a small amount of Mg, Fe, S, etc. It represented the scale characteristics under the downhole conditions of pressure and temperature without the influence of scale inhibitor. The scale crystals produced from surface pipeline were calcite in form of crystal rhombohedron and aragonite in form of acicular and columnar shapes, both of which distributed alternately. The main elements of scale products included O, Ca, C and a small amount of Mg, Fe. This phenomenon showed that the scale inhibitor prevented aragonite from changing into calcite. The characteristics comparison of calcium carbonate scale in the surface pipeline and the underground string offered a typical case for the mechanism studies on influences of crystal growth characteristics by scale inhibitor.