A system based on wide-band light source and Fabry-Perot (FP) structure is introduced for the detection of CO2. The system is an active optical system with simple structure and high signal noise ratio (SNR). Based on the principles of traditional differential absorption lidar, the basic working principles of the detection system are described, and the system parameters are designed by using the HITRAN database to simulate the atmospheric environment. Thus the working band of the system is determined to be 1.57μm, the light source is a L-band super-luminescent LED (SLED), and the energy fluctuation value Rip is 50dB. The system output power is 24.51mW, and the filter at the receiving end is a fiber-optic FP cavity filter with the center wavelength of 1.55μm, the bandwidth of 60nm, and the channel interval of 50GHz. The error of the designed system is only 2×10-6.