LAM400 is a geomagnetic atomic magnetometer based on the principle of radio-frequency (RF) resonance. It achieves high-sensitivity detection of the Earth's magnetic field by measuring the atomic response at the Larmor frequency. The system integrates laser frequency stabilization, an atomic vapor cell, RF coils, and a heating module, featuring high sensitivity and low noise. It is suitable for applications such as geomagnetic measurement, navigation, geological exploration, and weather forecasting.