Leveraging the unique properties of wireless optical channels can enhance secure and efficient high-speed communication between satellites and ground stations through optical key generation and distribution. This paper examines the correlation of adjacent sub-channels in a wireless optical channel spatial multiplexing key generation system. A MIMO model is constructed using phase screens created by power spectrum inversion based on Kolmogorov atmospheric turbulence, simulating Gaussian beam propagation through atmospheric conditions via Monte Carlo methods. We analyze the impact of varying turbulence intensities, transmission distances, and beam diameters on optical intensity distribution, as well as their effects on the correlation between adjacent sub-channels considering factors like turbulence intensity, distance between receiving apertures, aperture sizes, transmission distances, and optical wavelengths. The findings indicate that the correlation of optical signal power received by adjacent apertures increases with the diameter and wavelength of those apertures but decreases with the distance between them, transmission distance, and turbulence intensity. In near-ground horizontal link scenarios with an atmospheric refractive index constant $C_n^{\mathrm{2}}$=5×10^-14 m^-2/3, a receiver aperture radius of 0.015 m, and a transmission distance of 2 000 m, the correlation of optical signal power between adjacent channels is nearly zero at a distance of 0.07 m, suggesting the independence of the two channels. These insights can improve the performance of optical channel key extraction systems in atmospheric conditions.