The long corridor surge chamber has been widely applied in mixed hydropower development,its long corridor is divided into independent pressure regulation system by partition wall in the chamber.The different schemes of partition walls has a significant impact on the safety of construction, reliability of operation as well as invest.The design scheme of structure should be reasonably optimized.Taking a large long corridor surge chamber as an example, the paper analyzed the advantages and disadvantages of tow different design schemes in stability of surrounding rock, convenience of construction and investment of project. The result indicated that rock column of good integrity has obvious advantages to strength the stability of surrounding rock in period of construction and the stability of chamber structure in period of operation. Combined with the consideration and economic factors, the optimal program is scheme I.