The compositional quantification analysis for series samples with molecular formula of (PrGdYbBi)3(FeAl)5O12 (multi-substituted epitaxial yttrium iron garnet film on gadolinium gallium garnet substrate) is processed with EPMA. The self-made oxide standard samples are tested and used. During measurement, the influence of the substrate, interference between X-rays emitted from different element and poor uniformity of samples are took into account. The ZAF correction is also processed. The whole error is less than 3.5wt%, and the precision for single element is better than 2wt% comparing with samples with exactly known composition.