By heating up the T_β temperature and then holding 25-90s, the semi- equiaxed structure, which is a transition structure between the equiaxed structure and the lamellar structure,is shaped. The influence of the change of heat holding time on the semi-equiaxed structure evolution law and mechanical properties is studied. Experimental results indicate that the formation of the semi-equiaxed structure is mainly because the element Mo into the β matrix diffused inhomogeneous into primary equiaxed α phase when specimens was kept above the T_β temperature for a short time,And in the cooling process,the β transformain structure grow through the primary equiaxed α phase.With the prolongation of holding time,the semi-equiaxed structure are gradually replaced by lameller structure.When heated to 1015℃,hold 45s,the tensile strength is 1219MPa,the reduction of area is 29%,and the elongation is 14%,which has a better strength and plasticity.