The population of china is one fourth of the world's.中国的人口是世

可以改善一下.
The population of China is one fourth of that of the world.(第二个that指前面的人口）.
或者
China has a quarter of the world's entire population.
再问： The population of china is one fourth of the world's.这句话里the world's我在world后面直接用逗号S，可以吗？
再答： 所有格的问题，the world's population基本上等于 the population of the world，所以你用了's那后面就要再加population，这样又出现重复单词的问题了，所以不要这样用。