The invention discloses an intelligent ammeter serial port DL/T645 communication protocol online fast detector which belongs to the field of communication and control of intelligent ammeters and particularly relates to an intelligent ammeter serial port DL/T645 communication protocol online fast detector, which can improve work efficiency of field debugging personnel. The detector includes a transformer, an ISL3152 chip, a 485 interface, an MCU and an indicating lamp. Key points of the structure of the detector are that an input port of the transformer is connected with the commercial power; an output port of the transformer is connected with an input port of a rectifier bridge; an output port of the rectifier bridge is connected with an input port of a three-terminal voltage regulator block; an output port of the three-terminal voltage regulator block is connected with a power input port of the ISL3152 chip and a power input port of the MCU; and a 485 transmission port of the ISL3152 chip is connected with a 485 transmission port of the MCU.