Please recommend some law firms with branches in Chengdu and Zhangjiagang. . . Just like Dacheng Law Firm. . I really appreciate it．

This doesn't exist. Dacheng doesn't even have a branch in Zhangjiagang, but only in Suzhou. If you want to have such a big office, it will usually be located at the provincial level or in a relatively developed city. If there are branches in both places, King & Wood Law Firm has another branch. You can also check a law firm like Guo Hao.