In this article, it studies the effect of TC4 - DT titanium alloy''s triple heat treatment on microstructur-e after thermal deformational at high temperature. It shows that the first temperature and the second temper-ature which in the triple heat treatment influenced the amount of alpha phase in alloy microstructure, m-oreover ,with the increasing of the first temperature and the second temperature, equiaxed alpha phase w-ould gradually decease. The tri-modal structure which results from 940℃?h WQ 920℃?h WQ 820℃?.5h AC, which consists of about 20% equiaxed alpha, 50%~60% basketweave formed by striature alpha and transformed beta matrix.Further more, there are smaller secondary strip alpha among first strip alpha in the basketweave which formed by striped alpha, the microstructure has a smaller aspect ratio and the alpha staggered cluster that refined the microstructure.