Downhole tool, signal transmission system and signal transmission method

Disclosed are a downhole tool, a signal transmission system and a signal transmission method. The downhole tool comprises a downhole tool body, a circuit compartment and a first signal transmission module. The circuit compartment is 5 arranged in the downhole tool body, and a plurality of circuit modules are mounted in the circuit compartment. The first signal transmission module is arranged at the downhole tool body, the circuit modules are electrically connected to the first signal transmission module, the first signal transmission module is used for being in communication connection with a second signal transmission module, and the second 10 signal transmission module is adaptive to the first signal transmission module. At least one circuit module comprises a first carrier communication control unit, through which the circuit module can receive or send communication signals. The downhole tool can ensure airtightness in a severe downhole environment to protect the circuit modules from invasion, and establishes a connection with the outside quickly by 15 means of an inductively coupled power transfer technology and a carrier communication technology to perform operations such as program configuration upgrading and data uploading on the circuit modules.