The present invention relates to an online game system and online game processing method. The online game system comprises a client terminal and an online game server communicating with the client terminal via a communication network. Updated data of the online server is converted into usable common program library of the client terminal. The updated data is transmitted to the client terminal. The client terminal modifies at least one of client terminal game program and client terminal game data. The client terminal may not communicate with online game server when indicating operation input by using sub game data, but control said online game execution with the client terminal game program recorded in a recording unit or client terminal game data. The invention reduces communication traffic load of the online game server and reduces operation load of the online game supplier.