In an active distribution network (ADN), the function and performance of a Feeder Terminal Unit (FTU) need to be improved and expanded. In this paper a multi-agent system (MAS) FTU based on deep-merging of primary and secondary equipment is proposed. The proposed FTU includes four parts: a wide-band voltage sensor, a wide-band current sensor, an analog to digital converter and control output unit (ADCU) and a main control unit (MCU). Among them, ADCU is responsible for data acquisition, electric energy metering and the conversion of switching control commands. The MCU with a Beidou /GPS receiver undertakes the tasks of PMU, fault identification, fault isolation and wireless communications. High-speed optical fiber communication is adopted for the data exchanging between the MCU and the ADCU, in which the communication protocol can be flexibly selected or customized. The only electrical connection between the MCU and ADCU is for working power supply, and this eliminates the electrical connection loop and effectively improves the anti-interference ability. The system structure of the proposed multi-agent FTU, the wide-band voltage sensor based on Wien bridge circuit, and the wide-band current sensor with iron core and air gaps are designed in detail. The key aspects studied are the construction method of the MAS environment, the design of the MAS synchronized coordination mechanism, and the design principles and structures of specific function agents. The proposed technical scheme fulfills the design concept of integration and intelligence of distribution automation equipment, expanding the functions of the FTU, improving the performance of the FTU, and providing a new idea for research in the field. This work is supported by the National Key Research and Development Program of China (No. 2017YFB0902800).