Abstract: The thermal-stable particles of oxide containing Ca can be formed in micro-calcium steel which can be obtained by appending Si-Ca powder into carbon steel.The microstructure, γgrain size, strength and toughness of coarse grain heat affected zone(CGHAZ) in micro-calcium and no micro-calcium steels were studied by SEM, microscope, tensile test and series impact experimental.The research show that the second phase particles have strong pinning force to γgrain boundary of CGHAZ in micro-calcium steel.It can retard γgrain growth in the course of welding, and fine γgrain in the CGHAZ, and improve the strength and toughness of CGHAZ in micro-calcium steel.