In this paper, computational analysis of 3D gravity Anomalies in Cartesian and Geographical Coordinates is considered. We must along-consider the Earth's curvature with the 3D Gravity computations for very large model geometry. If the bodies have very large edges lengthens, for example, over a few thousand meters. The Earth's curvature plays a large role with the definitions model geometry and/or with the computations as seen in Fig. 1. They affect the results very strongly. We cannot along- consider Earth's curvature with 2D Gravity computations and also with the 3D Gravity computation in cartesian coordinates. We can along-consider it only with the 3D Gravity computation, in geographical coordinates. We have computed it with the 3D Gravity anomaly for same model geometry in two different coordinates system; in cartesian and also geographical coordinates as seen in Fig. 9 and 10. The comparison clearly shows from the two results, how large the differences (as seen in Table 1) are. Computed Gravity anomaly exactly centered over the body is 430, 47 mGal in geographical coordinates and 415.86 mGal in Cartesian coordinates. The difference between the two sizes is 10, 73 mGal and that is not to be neglected.