If you plan to apply visa from the Chinese embassy/consulate in the country of your citizenship, a signed invitation letter from CMS of Zhejiang University is all you needed from the conference organizer. For other supporting document, please consult the website of the appropriate Chinese embassy/consulate.
If you plan to apply visa from the Chinese embassy/consulate in the country NOT of your citizenship, an official invitation letter from the office of foreign affair at Zhejiang University is (sometimes) required. If you need such a letter (for invited participants only), please contact email@example.com the end of April. It takes several week to obtain this letter.
If you have any question, contact Sun: firstname.lastname@example.org