For designing the stable communication system at future mmWave bands, the prediction method of the obstruction losses is necessary. In this research, the line-of-sight obstruction losses caused by rectangular-shape metal plane and human-shape metal plane were measured at 66.5 GHz in anechoic chamber room and the accuracy of knife-edge diffraction method (KEDM) and physical optics (PO) were valiated. It was concluded that PO can predict shadowing loss caused by human-shape metal plane with complex geometric shape.