The effects of process parameters on the microstructural evolution, including grain size and volume fraction of the α phase during hot forming of a TC6 alloy were investigated using compression tests. Experiments were conducted on the material with (α + β) phases at deformation temperatures of 800, 860, 920, and 950°C, strain rates of 0.001,0.01, 1, and 50 s-1, and height direction reductions of 30%, 40%, and 50%. After reaching a peak value near 920°C, the grain size and volume fraction decrease with further increase of deformation temperature. The strain rate affects the morphologies and grain size of α phase of the TC6 titanium alloy. At a lower strain rate, the effect of the strain rate on the volume fraction is greater than that at a higher strain rate under the experimental conditions. The effects of the strain rate on the microstructure also result from deformation heating. The grain size of the α phase increases with an increase in height direction reduction after an early drop. The effect of height direction reduction on the volume fraction is similar to that of the grain size. All of the optical micrographs and quantitative metallography show that deformation process parameters affect the microstructure during hot forming of the TC6 alloy, and a correlation between the temperature, strain, and strain rate appears to be a sig nificant fuzzy characteristic.