Platinum nano clusters, which are attractive material for highly activated catalysis, are usually evaluated by scanning tunneling microscopy (STM). Here we challenge to evaluate the structure of Pt nano clusters by reflection high-energy electron diffraction (RHEED) for the first time. The nano cluster models are made of n = 7 and n = 15 Pt atoms, which are deposited on TiO2 (110) substrate. The former has two dimensional (planer) and the latter three dimensional (two layer's) shapes. They are rotated around their  axes of Pt crystal, whose axes are also inclined from the substrate surface normal because of the atomically rough substrate surface. The RHEED patterns have been calculated by kinematic diffraction theory. From the calculated patterns for the two types of the clusters (n = 7 and 15), it is found that there is characteristic difference in the radial intensity distributions. The difference is attributed to existence or absence of the higher order reflections which arise from two layers of Pt(111).