Experimental and numerical results concerning the flat punch indentation to semi-infinite body with partially constrained free surface are presented The distributions of slip line directions are predicted by Moire fringe analysis using Vinckier"s method. A mumerical study is made of the same problem by finite element method and the results are compared with the experimental results. It is shown that the contour feature of possible slip line field is similar to that of well-known Prandtl indentation sloution.