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Southern China is the nation’s major grain-producing areas. In recent years, under the background of global climate change, regional drought disasters have been increased, and caused serious agricultural drought loss and obvious anomaly characteristics. However, the variation characteristics of agricultural drought loss and drought hazard mechanism are still unclear in south China, which seriously affects the in-depth understanding of southern agriculture drought and its assessments. Therefore, based on agricultural drought disaster conditions, crop acreage, meteorological drought monitoring index and conventional meteorological factors and other related data, systematical and comprehensive agricultural drought loss rate variation and its relationship with climate-formative factors have been analyzed in recent 50 years. Agricultural drought comprehensive loss rate is used as an agricultural drought disaster or risk characteristics loss severity index. Agricultural drought comprehensive loss rate is an integrated index that can reflect severity of loss caused by agricultural drought disaster and established by drought-affected crop planting area at different levels and planting area. The results showed that comprehensive agricultural drought loss rate increased obviously and with a rate of about 2.5%, the relative increased rate reached to as high as 80%. Agricultural drought disasters loss has been increased seriously and doughty disasters risk also has been increased more higher than before, southwest is more apparently than south and southeast. With respect to spatial distribution, probability of climate tendency rate for comprehensive loss rate in south China ranges from 0.1%/10 a to 1.8%/ 10 a. In addition, increase in climate tendency rate in the southwest is more obvious than that in the south and southeast. And, as a result of crop growth stages on the climate elements in dependence on different season and climate factors of non-uniform distribution characteristics, agricultural drought loss rate is mainly affected by key period meteorological drought and the effects of climate change, mainly precipitation and temperature. As for precipitation, 6 months including April, May, June, July, August and October serve as key impacting periods. As for temperature, 5 months including January, June, July, August and October serve as key impacting periods. As for MCI, only two months including July and August serve as key impacting periods. But other climatic factors change is not obvious influence on agricultural drought loss rate. In south China, key impacting periods of MCI coincide with key growth phases of most crops; common key impacting periods of temperature and precipitation coincide with major growth phases of most crops in south China; key impacting periods of precipitation coincide with major or key growth phases of some crops; while key impacting periods of temperature coincide with key periods for overwintering of winter wheat. As a result, the fitting relationship between the south agricultural drought loss rate and the critical period climate factor is much better than its relationship with throughout annual climate, and more key climate factors has more obvious advantages in fitting relationship compared with single factor. Such multi-factor relationship can not only describe the disaster-causing effect of meteorological drought, but also reflect the roles played by severe evapotranspiration and soaking rain processes on drought disaster-causing process. Meanwhile, the agricultural drought loss assessment model with multiple factor relationship had been done for cross validation method, correlation, error level and reliability are the relevance of the ideal, which indicated that the model is an optional reliable and objective model for evaluating the impact of drought disasters on agricultural yield in south China or estimation on risks of agricultural drought disasters in future climate scenarios. The study results have important scientific reference significance for the development of south China agriculture dry drought damage assessment method.