Although coherent twin boundary (CTB) migration in fcc metals has been widely studied, little is known about the CTB migration behavior in the binary transition-metal nitrides system (e.g. rock-salt CrN). Using in-situ atomic-resolution electron microscopy, we report two different twin boundary defect (TD) nucleation and CTB migration modes at the CTB/ITB (incoherent twin boundary) and CTB/surface junctions. A new twin defect nucleation and CTB migration mode are observed from the CTB/surface junction. We show that such CTB migration is associated with a boundary structure alternating from an N-terminated to Cr-terminated, involving Cr and N atom respective motion, i.e., asynchronous CTB migration. We further reveal the dynamic and thermodynamic mechanism of such asynchronous migration through strain analysis and DFT simulations. Our findings uncover an atomic-scale dynamic process of defect nucleation and CTB migration in a binary system, which provides new insight into the atomic-scale deformation mechanism in complex materials.