Based on the extended Huygens–Fresnel principle and infinitely long phase screen, the scintillation index and the aperture averaging effect of partially coherent beams in computational ghost imaging (CGI) with a finite bucket detector through atmospheric turbulence is investigated analytically and numerically. The signal–to–noise ratio (SNR) is used to evaluate the image quality of computational ghost imaging. It is found that a strong phase modulation effect due to increasing turbulence intensity, leads to a degradation in image quality, as well as an increase in the scintillation index. In addition, the scintillation–saturation phenomenon occurs for strong turbulence. On the other hand, reducing the propagation distance, and the degree of source coherence results in a decrease in the scintillation index and an improvement of image quality. However, deteriorating the degree of beam source coherence could weaken the aperture averaging effect. Thus, the optimal beam and bucket detector aperture size require a trade–off between the scintillation index, the aperture averaging effects, and the image quality in CGI.