The embodiment of the invention discloses an account application method, a building method, relevant equipment and a system. the account application method comprises steps: a client acquires a mobile payment account application request inputted by a user; the user is detected whether to have a usable electronic cash account already; if the user already has a usable electronic cash account, the mobile payment account application request is sent to a server; information that the mobile payment account is built to the user returned by the server is received, and the server binds the mobile payment account built to the user and the usable electronic cash account already owned by the user; and the received mobile payment account information is written to a safety chip. According to the embodiment of the invention, offline payment can be realized, safety of capital is improved, and inconvenience brought by maintenance and use of multiple electronic cash accounts can be avoided.