Evaluation of antithrombogenic property of cardiovascular devices, such as a ventricular assist device, is important at the design stage of development. Although animal experiments and animal blood experiments are conventionally performed for design evaluation, they required costs and periods of time. Thrombus mimetic testing method was proposed for mechanical ceirculatory support devices. In the method oil paint and surfactant were suspended in water and the resulting adhered paint was observed. In this study we applied the method to a centrifual blood pump to investigate the effect of washout holes on thrombus formation, using models of partially closed washout holes. The result was that paint adhered at the leading edge on impeller front side and at the rings of no relative velocity on impeller rear side. The results were similar to proceeding animal studies.