German Aerospace Centre released TanDEM-X 90 m (TDM90) global digital elevation model (GDEM) as freely available in October, 2018 and declared that it describes all Earth's landmasses pole to pole with 1 m absolute height accuracy which could not been achieved by previous space-borne GDEMs. In this study, the coherence level of TDM90 with SRTM90 and ASTER90 were comprehensively analysed by visual and statistical comparison approaches in two study areas including different topographic characteristics. In visual approaches, colour-scaled coherence maps, contour maps, aspects depending on ascending and descending flying orbits and outlier illustrations were generated and interpreted. In statistical approaches, horizontal and vertical absolute and relative geolocation disparities and frequency distributions of height differences were presented. The results demonstrated that the terrain slope has a great impact on the coherence levels between TDM90 and compared GDEMs. Overall, TDM90 is more coherent with SRTM90 against ASTER90 except clear dissimilarity problems in strip border lines.