The invention relates to an on-line leakage detection device for a tube type heat exchanger, belongs to the field of tube type heat exchanger detection equipment, mainly solves the problem of how to check whether a heat exchange tube is damaged and leaks or not when raw material gas and liquid exchange heat with a heat exchange tube in a shell for cooling, the device comprises a detection body and a hose, and a liquid inlet is set at the back of the detection body; a liquid storage chamber is arranged in the detection body, the liquid inlet is communicated with the liquid storage chamber, a pump is arranged in the liquid inlet, one end of the hose is connected with the liquid inlet, and the other end of the hose is provided with a connector. A PCB is arranged in the detection body, an amplification circuit, a filter circuit, an AD conversion circuit and a micro single-chip microcomputer are arranged on the PCB, two electrodes are arranged on the inner wall of the liquid storage chamber, and the two electrodes are connected with the amplification circuit through circuits. In the invention, the detection process is standard and reasonable, the detection result is scientific and effective, the device is small and portable, a charging mode is adopted, and the device is convenient to carry to the actual working scene of the heat exchanger.