A phased low temperature occurred in the summer of 2009 in Heilongjiang Province, resulting in a steriletype rice cool injury, during which the field crops had varying degrees of delayedtype cool injury and fertility postponement. Through calculating the daily cool accumulated temperature according to its relationship with the rice emptygrain rate and the probability distribution of the number of sensitive rice groups during sensitive periods, the rice emptygrain rates and loss rates caused by the steriletype rice cold injury are assessed by means of the daytoday and hourtohour mean temperature from June to August 2009. On the basis of the clear physiological responses of rice to low temperature and cool injury, the assessment method is described, from the view of the dynamic temporal changes of rice during sensitive stages, which is superior to the assessment methods of adopting average temperature or temperature anomaly as indicators and can improve the precision and quantification of assessment.