The present invention provides a method for game data transmission, including: acquiring, by a client upon logging into a server, a session key assigned by the server; encrypting game data with the session key, and submitting the encrypted game data to the server; decrypting and verifying the received game data by the server, and saving the game data if the game data are proved to be valid. The present invention also provides a system, client apparatus, server and mobile terminal including the client apparatus to which the preceding method can apply. The method, system and apparatus of the present invention ensure that the client can transmit game data safely to the server and protect the game data from being tampered with or counterfeited.