As a special form of magnetic field,alternating magnetic field has a wide range of applications and academic value. At present,there is no proven method for absolute measurement of alternating magnetic field. Pump detection atomic magnetometer has a wide range,high sensitivity and can accurately reflect the real characteristics of magnetic field,which is of great significance in magnetic field measurement and calibration. Through the research on the action mechanism of the pump detection atomic magnetometer excited by the alternating magnetic field,the absolute measurement of an alternating magnetic field by the pump detection atomic magnetometer is achieved through the improvement of the experimental. And the measurement of an alternating magnetic field with a background magnetic field of 40,000 nT,a frequency of 100 Hz and an amplitude of 1000 nT is achieved in the Z axis direction；the measurement of alternating magnetic field in the Y axis direction with a background field of 1000 nT,a frequency of 20 Hz and an amplitude of 500 nT. The results show that the experimental device is suitable for the measurement of alternating magnetic field at low frequencies and weak magnetic field strengths,and the method provides a practical technical tool for the measurement and calibration of alternating magnetic field.