This report shows an analysis of a compression casting method, which is used to prevent internal cracks of a slab in an unbending zone of a continuous casting machine. To investigate the behavior of a slab during a compression casting, a numerical calculation method was developed. Using this method, stress and strain in a solidified shell of a slab were calculated and the following articles became clear: (1) When compressive forces in the casting direction act on a slab in an unbending zone, mutual effect between unbending forces and compressive forces appears and stress and strain on an inner surface of a shell of a convex side change from tensile to compressive. (2) Among various casting parameters, the parameters which have large influence on the effect of a compression casting are an amount of compressive forces and temperature of a slab.