An experimental device is created by using Hall sensors，HC-05 bluetooth module，and STM32 microcontroller，which is capable of measuring weak magnetic field intensities and presenting measuring results in real-time on a smartphone．The operating principles of the device are explained in detail．By conducting multiple magnetic field measurement experiments at various positions and with differing coil turns，we collected extensive experimental data． Through the analysis and processing of the data，it is determined that the measurement range of the magnetic field detection device is ± 40 GS and its resolution is 1 GS． Through analysing the uncertainty，the practicality and scientific validity of the device are confirmed．Furthermore，when compared to other electromagnetic field detection instruments—characterized by higher accuracy and broaderdetection ranges this magnetic field measurement device offers advantages such as lower cost and ease of operation，making it more suitable for meeting the general public＇s magnetic field measurement requirements．