Abstract: For the requirements of the latest DL/T 618-2022 testing procedure of loop resistance of GIS equipment and the development of intelligent testing system, a development scheme of handheld 300 A loop resistance tester combined with intelligent cloud APP was proposed. The high power constant current source was realized through intelligent switching power supply. The MOSFET provided stable gate-source voltage for the power device to keep the current stable. The sampling increment was quantized and encoded by the ∑-△ analog-to-digital converter to realize the high-resolution extraction of the linear pulse code modulation digital signal. And the temperature detection module was designed to achieve accurate testing in different environments. Real-time control of the tester, data report generation and equipment maintenance can be achieved by scanning the QR code through the intelligent cloud APP and relying on Bluetooth signals. The slope of the loop resistance data set between tester with benchtop equipment was close to 1. And the intelligent cloud APP can realize the rapid control response to the tester and generate reports, which indicated proved that the developed equipment processed excellent convenience and reliability.