The experiment of paddy crack additional percentage (CAP) subject to various drying condition (drying conditions) including hot air temperature , relative humidity and drying time was done. Taking drying constant K as the media, the mathematical model between drying conditions and crack additional percentage was developed as follows: Ｃ＝６．６４９＋０．４５３ｔ＋（６．７４９＋０．１５０ｔ）［１．７４６－０．０３９（ＲＨ）－５７．９７４／Ｔ］. Its validity was checked by comparing simulated and experimental values.