A foam-irregular-sea-surface hybrid model is established based on the quantum properties of photons and with the consideration of the influences of the foam particle size distribution, scattering coefficient, foam layer thickness, incident angle and wind speed. The error rate formula for an air-water quantum key distribution (QKD) system is obtained. Combining with the Monte Carlo algorithm, the influence of each parameter on the photon polarization state, QKD error rate and transmission distance is simulated and discussed. The performance of the four-intensity BB84 air-water QKD system under the foam-irregular-sea-surface is analyzed. The research results show that, the polarization error rate increases with the increase of the foam layer thickness, scattering coefficient and light incident angle. Besides, the increase of wind speed leads to the rise of the quantum bit error rate of the air-water QKD system and the reduction of the secure transmission distance. Meanwhile, the key generation rate and the secure transmission distance of the air-water QKD system decrease as the foam layer thickness increases, and the maximum secure distance is reduced from 144 m to 101.3 m when the foam layer thickness increases to 6 cm and the maximum polarization error rate is considered, but it still satisfies the requirement of the 100 m safety depth for the underwater vehicles.