Abstract: This paper has the following contents.(1) Discussing the development of man's knowledge about climate from five aspects, the concept of Climate-origin of history, perceptual knowledge, relatinships between climate and weather or between climate and geography and the climate-forming process;(2) Summarizing the concept of climatology and dividing it into four field——statistical climatology, synoptic climatology, geographical climatology and dynamical climatology;(3) on the basis of criticizing the long prevailing definition suggested by E.C. and advancing a new definition of climate- "Climate is a macroscopic atmospheric physical process";(4) Unequivocally pointing out that "climatology" is not a branch of geography, but is juxtaposed with it in the classification of science.