CT25 special friction welding machine is used to weld 35CrMnSi/T3 with different inertial flywheel rotation speeds.The interface microcosmic binding characteristics and microstructure changes are observed by SEM.The element diffusion near the interface is detected by EDS and the microhardness of plastic deformation zone in Cu matrix is tested.The results show that,when the inertial flywheel rotation speed increases,friction heat of primary pressure increases significantly,more plastic deformation forms between the contact surfaces by secondary pressure,and bonding of work pieces is promoted.When the flywheel rotation speed is 3 000 r/min,the joint of 35CrMnSi/T3 by inertial radial friction welding process gets clean binding domain,elements obviously diffuses,the finegrain αFe and εCu structure forms in recrystallization zone and the welding effect is good.The microhardness of interface region in Cu matrix is increased by violent plastic deformation.