Abstract: In order to meet the requirements of high cycle fatigue performance after impact damage of materials used in engine primary disk, the fatigue behavior of TC4 titanium alloy after external material damage was studied. TC4 titanium alloy samples containing three kinds of foreign object damage were prepared by air cannon method and the damage size was calculated. Fatigue tests were carried out on the samples without impact damage and with foreign object damage. The S-N curve was obtained and the initiation position of fatigue crack was observed. The results show that higher impact velocity and larger projectile diameter lead to larger FOD damage. The location of crack initiation is changed by external impact. By comparing the damage size statistics with the fatigue performance, it is found that the damage size in the width direction is the most important factor affecting the fatigue life.