The author has positive and negative attitudes respectively for the defensive role of the Great Wall,thus extends other usages and meanings,and we can see from all these usages and meanings the author's emothion tendency for the Great Wall.
Finally,we got the conclusion:Song Dynasty was more dependent on the defensive role of Great Wallthan Tang Dynasty,while Great Wall poems in Tang Dynasty were more critical than those in Song Dynasty.
It mainly analyzes from the differences of Tang and Song dynasties in political environment,cultural environment and situations of the countries.