The division is based on 1, political status 2, economic strength 3, city size 4 and regional radiation.
Extended data:
First-tier cities: Beijing (national political, cultural and educational center), Shanghai (national economic center), Guangzhou (economically developed, South China economic center, Guangdong provincial capital) and Shenzhen (economically developed, SAR city).
Second-tier cities?
Second-line strength
Hangzhou, Nanjing, Jinan (economically developed, sub-provincial and provincial capital cities), Chongqing, Tianjin (municipalities directly under the Central Government), Qingdao, Dalian, Ningbo and Xiamen (economically developed cities under separate planning)?
Erxianzhong
Wuhan, Shenyang, Chengdu (regional center and sub-provincial level with good economic development), Xi, Changchun, Harbin (regional center and sub-provincial level), Suzhou, Wuxi (the most economically developed prefecture-level city), Changsha, Fuzhou, Zhengzhou and Shijiazhuang (regional center and provincial capital with good economic development)?
Second-line weakness
Foshan, Yantai, Dongguan (economically strong cities), Taiyuan, Hefei, Nanchang, Nanning and Kunming (regional centers, provincial capitals of prefecture-level cities) (important economic cities)? Hohhot, Lanzhou, Urumqi, Guiyang (provincial capitals), Quanzhou, Zibo, Nantong, Wenzhou and Tangshan (emerging cities with strong economies).
third-tier city
Three lines
Haikou, Changzhou, Handan, Shaoxing, Daqing, Baotou, Taizhou, Anshan, Zhongshan, Zhuhai, Shantou, Weihai, Taian, Jilin, Liuzhou, Dongying, Zhenjiang, Jining and Xuzhou?
Sanxianzhong
Lhasa, Linyi, Yinchuan, Xining, Baoding, Qinhuangdao, Cangzhou, Ordos, Yangzhou, Dezhou, Taizhou, Luoyang, Ganzhou, Jiujiang, Binzhou, Huzhou, Jiaxing, Jinhua, Guilin, Huizhou, Zhanjiang, Jiangmen, Maoming, Zhuzhou, Yueyang, Hengyang, Yichang, Xiangyang, Kaifeng, Xuchang, Pingdingshan and Pingxiang.
Weak third line?
Dandong, Wuhu, Bozhou, Liaoyang, Jinzhou, Yingkou, Baoji, Xianyang, Huludao, Chengde, Xingtai, Zhangjiakou, Lianyungang, Datong, Yulin, Yan 'an, Karamay, Kashgar, Shihezi, Nanyang, Puyang, Anyang, Jiaozuo, Xinxiang, Zaozhuang, Liaocheng, Bengbu, Huainan, Maanshan, Lishui, Quzhou and Anqing.
All the remaining cities above the prefecture level in the fourth-tier cities.
References:
Baidu Encyclopedia-City Hierarchy