In order to explore influence of channel correlation on the signal scintillation in free space communications system with spatial diversity receiver and provide references for design of the sub-aperture size and its distribution, the expression of channel correlation coefficient of spatial diversity receiver under weak fluctuation conditions was deduced in theory. The relationship between channel correlation coefficient and signal scintillation with spatial diversity receiver was obtained. Channel correlation coefficient under both horizontal uniform and whole layer download non-uniform turbulent propagation paths was numerically studied. For the plane wave, there is an obvious negative correlation property between sub-channels for aperture receiver under non-uniform turbulent propagation path. For the spherical wave, it is similar for both turbulent non-uniform path and uniform path for aperture receiver; the negative correlation properties are not obvious.