The purpose of the present study is to know the influences of thermo-mechanical processing and heat-treatment on the prior b-grain size of TC4 titanium alloy, and the influence of grain size on damage-tolerance properties is also discussed. The average b-grain sizes under different thermo-mechanical processing and solution treatment conditions were measured. Noticeable difference of b-grain growth behavior was found between α+b forged and b forged TC4 alloy under the same heat-treatment conditions. The exponential relationship between b-grain size and solution time was presented. The results show that b-grain size does not always increase with increasing of solution-treatment temperature; a limit value of the grain size will appear in certain temperature region. For different forging process, the fluctuation of the prior b -grain size is different. This phenomenon is discussed in terms of grain growth thermodynamics and kinetics laws. Damage-tolerance properties results show that grain size has noticeable influence on fatigue crack growth rate and fracture toughness property.