In order to solve the problem of the residual noise of the probe light intensity in atomic magnetometer, a digital compensation method is proposed. Firstly, the basic theory of Larmor process detection is adopted, and the optical rotation angle of the linearly polarized light is detected through a photoelastic modulator and a lock?in amplifier. Then, the noise eater is used to obtain the compensation coefficient by sinusoidal modulating the probe light power and fitting the curves, and then the first harmonic component is post?corrected with the second harmonic component of the modulating frequency of the photoelastic modulator to realize the noise suppression of the probe light intensity. The hardware used for the amplitude modulation and even the primary light intensity stabilization device can be removed after obtaining the com? pensation coefficient, and the noise suppression can be achieved by using only the digital compensation technique. An atomic magnetometer based on K?Rb?21Ne vapor is bulit and carried out the experiment in the spin?exchange relaxation? free (SERF) regime, in which the results shows the noise of the optical angel detection signal is suppressed by 13.2 dB@ 3Hz. By applying the noise compensation method, the non?common mode noise caused by different optical paths is avoided, and the secondary stabilization is realized on the basis of the primary stabilization of the probe light in? tensity. The compensation coefficient can be calibrated regularly, and the influence from the change or instability of the system is reduced. The study is important for the sensitivity improvement of atomic magnetometers.