In order to clarify the causing mechanism of center cavity in the cast of high Cr steel, the casting experiment of cylindrical ingot in 1 ton scale and the analysis of thermal elastic-plastic stress and strain were carried out. Moreover in relation to these results, the influence of Cr and C concentration on the generation of center cavity was discussed with tensile strength just below the solidus temperature and solidification contraction of the specimens. As the result, though both center line cracks and shrinkage holes were observed in the center cavity of high Cr steel, difference of solidification contraction between specimens was not much. The primary factor of center cavity was proved to be cracking caused by thermal stress under the lower tensile strength just below the solidus temperature associated with the increase of the ferrite amount which should be influenced by Cr and C concentration. Therefore, it was indicated that laying compressive stress on the final solidification part was effective to reduce center cavity in the high Cr and low C steel.