Abstract: China is a major country of producing rice in the world. It can produce great social and economic benefits to decrease rice broken rate. This paper and some former researches indicate that the rice broken rate in the rice milling process has great relationship with the brown rice kernel cracking rate. So to reduce the rice broken rate, it is essential to decrease rice kernel cracking rate. Brown rice contains 75%±starch. The starch grain arranges in the cell wall of endosperm according to some kinds of crystal structure, between them is protein which affects rice strength and its quantity is different according to rice varieties. The rice tensile strength is between 9. 8×10⁵-9. 8×10⁶ Pa. The starch can expand when it absorbs moisture or being heated, and the humid coefficient of expansion is greater than that of temperature. So the rice grain can produce inner stress difference when it absorbs moisture or being heated, when the inner stress is greater than the tensile strength, rice kernel will crack, and they will break during hulling and milling process.In order to reduce rice broken rate, humidity and temperature should keep constant during the rice late ripening stage, drying and storage period, it should not be affected by tensile or bending strength during process period.