“省”（Province）是较大的行政区。 The word 省 is the abbreviation of "行省",which first appeared in 14th century. At that time, the government of Yuan Empire(1271-1368) divided the country into 10 “行中书省”(which means "the branch of the Executive Secretariat"), and then, it was abbreviated as "行省" ,"省". "郡"(Prefecture) 是古代的行政区名称。 The word "郡" first appeared during the Warring States Period (475BC—221BC), which means the border areas. After Qin reunified China in 221BC, the emperor divided his empire into 36 “郡”, and "郡" became the name of administrative districts. In the later centuries, "郡" became smaller and smaller, and finally be repealed in 6th century. "县" (county) 是较小的行政区，由省或市管辖。 The word "县" appeared during the Spring and Autumn Period (770BC—476BC), during that period, when the kings or dukes conquered a new territory, they would establish an administrative organization in the new territories, that was called "县". During the imperial period, the whole country has been divided into more than one thousand "县". Nowadays, "县" remains to be a basic level of the administrative system.

省和郡差不多是同一级的地域单位，但是省是行省制度后到现在使用的单位而郡是中国古代郡县制下的单位，而且省和郡所划分的地区各个历史阶段都不大相同。 县也是地域单位，划分的地域面积较小，在古代和现在还有不同。这里牵扯到了很多历史、政治的背景，总之他们都是划分区域的单位啦。

郡---- 中国古代行政单位，与现在的省差不多。Ancient Chinese called a province 郡 . We don't use this word nowadays. 省-----中国一级行政单位。China has 23 provinces today,such as Sichuan Province. 县-----中国三级行政单位。县 means a county in English,The province contains County.