Abstract: The transition process of grain boubary (G.B.) plate-like carbides have been researched in a Ni-base wrought superalloy under cyclic creep condition of temperature 1123 K, stress 392 MPa and hold time 8 (min). Its formative rule has been analyzed. Two kinds of different heattreatment method are used for getting different kinds of G.B. alloy, (straight G.B. and zigzag G.B.). The results of TEM analysis show that there are same process of transition particle carbides to plate-like carbides in both of G.B. alloy. There is a transition process from zigzag G.B. to straight G.B. before above process, i.e. the greater carbides which is not rule in size are broken up to particle G.B. carbides, (or straight process in brief). This process would take a long time. And so, the reason has been explained that plate-like carbides of zigzag G.B alloy are less than that of straiht G.B. alloy. A mode of transition zigzag G.B. to straight G.B. and of transition particle carbides to plate-like carbides is assumed in this paper.