In response to the issues of high cost, inadequate accuracy, and limited flexibility of weak magnetic field measurement devices available on the market, a three-dimensional magnetic field measurement device has been developed using PNI magnetic field measurement technology, centered around the RM3100 sensor. This device is capable of measuring magnetic field strengths at the nT level. Utilizing an ESP32 as the main control chip, it integrates modern communication technologies and cloud services to control servo modules, Bluetooth modules, Wi-Fi modules, and display modules, enabling real-time synchronous display of measurement data on both the device and PC, as well as precise close-range control of a three-dimensional mobile platform via a mobile phone. This enhances the device′s flexibility and potential application scenarios. Experimental results indicate that the device measures the Earth′s magnetic field strength to be 28.93 μT, with a measurement range covering ±800 μT and an error margin within 5%, while achieving a minimum measurement precision of 10 nT. The device is characterized by low cost, high precision, great flexibility, and ease of operation, making it suitable for various fields such as physics classroom demonstrations, experimental teaching, and non-destructive testing, with promising application prospects.