To study root curve induced by ,241,Am α-particle irradiation on ,Arabidopsis, embryos, molecular probe assay, outside-H,2,O,2, assay, ROS-extinguisher assay and root measurement assay are adopted. The study shows that root curve angles induced by ,241,Am α-particle irradiation on ,Arabidopsis, embryos have a positive relation (,r,=0.98) with irradiated doses within 100Gy. Root curve angle of 1Gy, 10Gy, 100Gy, and control is 13.3°, 28.7°, 69.1°, 12.5° respectively. Root of 100Gy treatment shows an "S" type curve while root growth is restrainded. Pseudo-color images of CM-H,2,DCFDA, which represents quantity of ROS in root tip, shows brighter in 100Gy irradiated group than that in the non-irradiated group. Root length and root gravitropism recover occurs when suitable concentration of scavenger of ROS is used. And root curvation has been observed while asymmetric replacement of H,2,O,2, used. The study indicated that α-particle-induced the change of root growth and root gravitropism might be due to ROS.