Erbium-doped fiber amplifier (EDFA), as a key device in the photoacoustic spectroscopy gas detection system, has a large impact on the system performance. Therefore, in this paper, we take CO as the target gas and study in detail the influence of EDFA on the second harmonic signal and the system noise value. In order to avoid the interference of CO2 and H2O in the air, we choose a laser with a center wavelength of 1567.3249 nm. On this basis, a CO photoacoustic spectroscopy detection system with EDFA as the core was constructed. The second harmonic output signals and system noise signals under different EDFA output powers were investigated when the light source was wavelength modulated. The results show that the amplitude of the second harmonic signal increases gradually from 0.5 W to 2 W of EDFA output power. The two are linearly positively correlated with a correlation coefficient of 0.996. The system noise also increases significantly from 0.5 W to 2 W, but the two are nonlinearly correlated. The maximum value of the detection system signal-to-noise ratio and the minimum value of the minimum detection lower limit are both at 1.5 W, which are 756.93 and 66.05 ppm, respectively.