Abstract: This paper is a part of the achievements of the book named"Documentary Catalogue Index of Oasis Re-search in China". Based on the study and synthetical analysis on the predecessors'achievements in oasis re-search, the new definitions of oases are given in the paper:Oases are the efficient ecological-geographical land-scape areas outstanding from their vicinities in the arid deserts, they have the stable water sources, luxuriantplants, vital living things, and certain spatial scale. The oasis systems and their main features are analyzed. Afterdiscussing the distribution of oases in the world, the oases in China are regionalized into three main areas, i. e., the Hetao Plain oasis area in east China, the arid continental oasis area in northwest China, and Qaidam Plateauoasis area, based on the differences of the regional geographical environment of oasis distribution in China, geo-graphical location, terrain, atmospheric circulation, climate, evolution of oases, and impact of human activities. Fi-nally, the oases in China are classified into four basic types, i. e., the terrace-typed oases along the rivers, fan-typed oases alluvial-plain oases, and delta oases, according to the basic factors of water, soils, etc. in the oases.

Key words: oasis area, basic type, efficient ecological-geographical landscape