中文摘要：

疫灾是由传染病大规模流行导致人类健康与生命损失的灾害。先秦两汉时期（公元前771～220年）见于记载的疫灾年份57个，疫灾频度5．74％。其中，春秋战国为1．64％；西汉为7．33％；东汉为15．90％；公元前二世纪为4％，公元前一世纪为9％，公元一世纪为12％，公元二世纪为15％。不排除疫灾记载有近详远略的可能，但从全国范围看，先秦两汉时期疫灾越来越频繁的趋势是客观存在的。疫灾发生的季节除秋季较少外，春、夏、冬季的概率差不多。在周期性规律上，该时期经历了2个大的疫灾稀少期和3个大的疫灾频繁期，第一个波动周期（公元前200公元前120年）约80年时间，波峰不很明显；第二个波动周期（公元前120~80年）长达2个世纪，其中公元前50～50年的疫灾频度高达17％，为两汉之际的疫灾高峰；第三个波动周期始于80年，东汉灭亡尚未结束，而是下接三国时期的疫灾高峰。在空间分布上，疫灾分布与入口分布有高度相关性，先秦时期仅黄河、长江流域有疫灾发生，西汉时期由于匈奴的介入，蒙新高原开始有疫灾记载，东汉时期南方入口大量增加，东南沿海开始有疫灾记载。总体来说，先秦两汉时期的疫灾是北方甚于南方，但随着时间推移，南方疫灾比重不断提高，反映了南方人口与经济的发展。

英文摘要：

An epidemic is an outbreak of a contractible disease that spreads at a rapid rate through a human population, directly threatening human health and life. From 771BC to 220AD, at least 57 years witnesses epidemics, with an average epidemic frequency of 5.74% （1.64% during 771BC-- 202BC; 7. 33% during 202BC-- 25AD, 15. 90% during 25AD-- 220AD; 4%before the 2nd century BC;9% in the 1st century BC; 12% in the 1st century AD; 15% in the 2nd century AD）. In research period, epidemics mainly occurred in spring, summer and winter, with low frequency in autumn. Although it＇s possible that the more recently epidemics occur, the more they are recorded, epidemic frequency showed an increasing tendency over a long term. This period witnessed 3 peaks and 2 troughsof epidemics. The first period （200BC--120BC） lasted around 80 years whose peak was not obvious, while the second period lasted as long as two centuries, peaking at 17% during 50BC--50AD. The third period, starting from 80AD, was the beginning of another peak after 220AD. As for spatial distribution, epidemic distribution was closely related population density. Before 202BC, the epidemics occurred in the Yellow River and Yangtze Valleys afterward, they were recorded to hit the plateaus of Inner Mongolia and Xinjiang, resulting from the invasion of the Huns. During 202BC--25AD, as population increased in southern China, epidemics occurred in southeastern costal areas. During the whole research period, the regions of epidemics covered mainly north China rather than south China. However, the increasing frequency in south China reflects the development of population and economy there.