Maxwell-Garnett effective medium approximation (MG-EMA) model is chosen to study Pd ultrathin film grown on Si substrate, as well as its growth on self-assembled monolayers (SAMs) modified substrate respectively. The general oscillator (GO) model with one Drude and two Lorentz oscillators is firstly applied to fix the optical constants of Pd. Compared with Pd bulk model, MG-EMA model with GO is more reliable to predict the film thickness verified by X-ray reflection test. The stable growth rate on Si substrate reveals our methods are feasible and the quartz crystal microbalance measurement confirms the stability of the ALD chamber. For Pd coverage, MG-EMA fitting result is similar to the statistical computation from scanning electron microscope when Pd ALD cycles are over 400, while large bias exists for cycles under 400, might be due to that air is not the proper filling medium between nanoparticles. Then we change the filling medium into SAMs as a comparison, better fitting performance is obtained. It is demonstrated that the filling medium between nanoparticles is important for the application of MG-EMA model. (C) 2015 Elsevier B.V. All rights reserved.