The boundary layer is the transition zone between the surface and free atmosphere. Because of its high level it is difficult to detect the refined structure of the boundary's top layer extensively. Generation and evolution of the atmospheric convective layer were simulated in laboratory convective water tank with the dimension of 150 cm×150 cm×60 cm. When the collision light beam propagated through the simulated atmospheric convective boundary layer, facula image data could be obtained which was used for spectral analysis. Based on the theory of light wave propagation in turbulent media, the scaling exponents could be given by the method of determining dimensionless interzone. It is found that the scaling exponents in the mixed layer are -8/3 under the condition of the homogeneous land surface, which is the classic value of the homogeneous turbulence. However, the scaling exponents highly depart from -8/3 in the beginning of experiments and in the end they are also close to -8/3 because of the vigorous convection.The average scaling exponents in the entrainment zone have relationships with the convective Richardson number. It is also found that the characteristics of the scaling exponent profile are consistent with the contour lines of heat flux profile and normalized light intensity variation profile.