The coadsorptive properties of some small molecules adsorbed on Pd(100) surface are investigated by taking the tight-binding model and the one electron approximation. The results show that (1) the indirect interaction between the two admolecules (or adatoms) on Pd (100) surface has an oscillatory behaviour with the decrease of the coupling strength between these adsorbates and the substrate, and (2) the existence of O2 or H2 affects the dissociation of NO on Pd(100). In addition, some adsorptive structures are derived from adsorbate-ad-sorbate indirect interactions. These results are compared with experimental results.