Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the energetics and the electronic structure of 3d impurity Mn and Cr in the kink on the (010) edge dislocation in bcc iron. The calculations of binding energies show that both Mn and Cr can stabilize the system containing kink. We also calculate the structural energy, the interatomic energy, the local density of states and the charge density difference. The results indicate that both Mn and Cr in the kink can enhance the interatomic interaction between the impurity atom and the neighboring Fe atoms due to the hybridization of impurity d-Fe d orbitals. The introduction of the Mn and Cr impurity leads to a strong pinning effect on the dislocation motion in bcc iron, which may explain the solid solute hardening of Mn and Cr.