Atomic magnetometer is a precision measurement instrument based on quantum technology. Due to its extensive application potential, it is becoming the domestic and worldwide cutting?edge research. Atomic magnetometer concerns many quantum theories, and a grasp of the basics is helpful to carrying out the magnetometer related work and going in for a deeper research in the related areas. The author summaries some of the elementary quantum physics involved in the atomic magnetometer, including optical pumping, light shift, optical detection, evolution of atomic polarization in magnetic field, and magnetic resonance, etc.