Systematic comparison between computer simulation results and those predicted by Scheutjens-Fleer (SF) self-consistent-field theory is presented for the adsorption of diblock copolymers from a non-selective solvent on attractive surface. It is shown that although SF is a mean-field theory, it can qualitatively describe the adsorption phenomena of diblock copolymers. However, systematic discrepancy between the theory and simulation still exists. The approximations inherited in the mean-field theory such as random mixing inside a layer and the allowance of direct back folding may be responsible to those deviations.