This study proposes an automatic laser frequency stabilization method using dualfrequency modulation transfer spectroscopy(DF-MTS) to overcome the limitations of conventional MTS methods, such as insufficient sensitivity of the error signal and difficulty in determining the laser lock status. In this method, a dual-frequency sinusoidal phase modulation is applied to the pump beam, and two resulting error signals are demodulated and combined to construct a highly sensitive dual-frequency modulation transfer error signal. Furthermore, a second-harmonic-signal-assisted discrimination strategy is introduced for laser lock status determination. By utilizing the second-harmonic component in the absorption signal along with the amplitude information of the error signal, this approach enables accurate judgment of whether the laser frequency is aligned with the absorption peak, thereby achieving automatic absorption peak identification and rapid lock status detection. Based on the full-hardware real-time signal processing technology of field programmable gate array(FPGA), a fully automatic frequency stabilization control module is designed, featuring dual-frequency error signals demodulation, second harmonic signal demodulation, identify, control, and monitor (ICM), scanning control, proportional integral derivative control (PID), and fast relocking functions. When the loss of lock is detected, it will quickly start the relock process, enabling fully automatic frequency stabilization control. Theoretical derivation and simulation analysis are conducted, and a laser frequency stabilization experimental system is constructed to validate the proposed method. Experimental results show that the DF-MTS method improves the sensitivity of the error signal by 20.24% compared with conventional techniques. Further verification via beat-frequency measurements using a femtosecond optical frequency comb confirms that the laser is successfully locked to the absorption peak of the 85Rb D2 line (F=2 → F′=3). The standard deviation of the frequency difference between the stabilized laser and the theoretical value of the absorption line is 17 kHz, and the relative Allan deviation reaches 1.09×10-11. Auto-relock experiments show that the system can monitor the locking status of the laser in real time and complete relocking within 40.192 ms upon detecting loss of lock, indicating excellent dynamic response and robustness.