As the greenhouse effect becomes more severe, high-precision detection of atmospheric carbon dioxide column concentration has become increasingly critical. Differential Absorption Lidar (DIAL) has been widely used in atmospheric detection due to its high sensitivity and high spatiotemporal resolution. However, traditional DIAL systems still face challenges, including the complexity of seed laser frequency stabilization and the instability of the λ_off laser. This paper proposes a system leveraging low-pressure absorption spectroscopy for frequency stabilization and electro-optical modulation for frequency shifting, enabling stable alternating output of λ_on and λ_off laser beams from a single seed laser. This approach simplifies the seed laser system of the DIAL and ensures the high stability of both λ_on and λ_off laser beams. The system uses low-pressure molecular absorption spectroscopy for frequency stabilization and electro-optical modulation for laser frequency shifting. In the constructed frequency stabilization system, the long-path absorption cell features a 640 cm absorption path length, a chamber temperature of 298 K, a pressure of 0.095 atm, and a CO₂ volume fraction of 78% in the gas mixture. By measuring the Optical Depth (OD) of CO₂ in the gas chamber, the laser frequency is locked at the CO₂ absorption peak (1 572.334 2 nm). In the frequency shifting system, the laser frequency is shifted by 10 GHz using electro-optical modulation, resulting in a laser beam that is stabilized at the CO₂ absorption valley. In the frequency stabilization system experiment, low-pressure absorption spectroscopy was employed to enhance the precision of frequency stabilization monitoring. Using the CO₂ absorption line as a reference, the long-path absorption cell was evacuated to low pressure, and frequency stabilization was achieved based on the maximum OD value. Results show that after stabilization, the laser wavelength remained consistently locked at 1 572.334 2 nm. The laser frequency jitter after system locking is shown, with a frequency stabilization accuracy of 3.43 MHz, corresponding to a precision of 0.028 pm. In the frequency shifting system experiment, the laser frequency was shifted using electro-optical modulation. A 10 GHz RF signal with a 90° phase difference was applied across the electro-optical modulator, and the operating point was controlled to maintain stability. The results show that the shifted laser frequency was locked at 1 572.251 1 nm and 1 572.416 1 nm. This paper proposes an optimized frequency stabilization scheme for the seed laser system of DIAL, aiming to achieve stable outputs of λ_on?and λ_off?lasers using a single seed laser. The experiment employed low-pressure absorption spectroscopy to stabilize the laser frequency, ensuring that the λ_on laser remains locked at the CO₂ absorption peak for an extended period with stable output. Then, electro-optical modulation is used to shift the frequency of the stabilized λ_on?laser to that of the λ_off?laser, which is subsequently output. Finally, the performance of the frequency stabilization and frequency shifting systems is tested, and the results show that both the λ_on and λ_off lasers exhibit high stability after stabilization. This paper provides a high-precision frequency stabilization solution for the seed laser system in CO₂ DIAL, laying a solid foundation for high-precision atmospheric CO₂ concentration detection using DIAL systems.