Abstract: The derivation of the calculation formula of geodesic curvature on curved surface is discussed in this paper.The directly derived calculation formula is obtained by means of vector outer product.Two derivation processes of the calculation formula of geodesic curvature and the derivation of the Liouville formula are demonstrated in the coordinate grid of the orthogonal curve.

Key words: geodesic curvature, orthogonal curve, coordinate grid；Liouville formula