In this study, we conducted an erosion resistance test against soil specimens where Phalaris arundinacea L. had been grown. Our final objective was to determine the erosion control effect of vegetation works against raindrops using a local seedling. Foreign herbaceous plants of Poa pratensis L. were used as the control reference. X-ray CT scan was used to observe the development status of root systems in the soil and measure the erosion depth after the test. The results indicate that the erosion resistance of Phalaris arundinacea L. by the stems, leaves, and root system is comparable to that of Poa pratensis L. However, the erosion resistance of only the root system was found to increase or decrease depending on the thickness of the roots and the amount of root system in the soil.