The present disclosure discloses a system and a method for developing a third-party application. The system includes: a vehicle-mounted device and a developer platform communicating with each other. The vehicle-mounted device generates a corresponding API according to a protocol analysis mode of a vehicle signal and API specifications, adds the API to a software development kit SDK, and sends the API to the developer platform. The developer platform publishes the SDK so that a developer can develop a third-party application according to the API in the SDK.