A finite element (FE) model was established to investigate the preforming process of TA15 titanium alloy complex component based on DEFORM-3D platform, and the influence law of forming parameters on the microstructure evolution and the equiaxed α grain size during performing was simulated and analyzed. Results show that the equiaxed α-phases are refined as deformation proceeds. With the increase of temperature, the primary α-phase grain size increases when deformed between 950 oC and 980 oC. The grain size distribution is inhomogeneous when deformed at 980 oC. With the increasing of the deformation rate, the primary α-phase grain size decreases. Forming at deformation rates of 0.5 and 1.0 mm/s, the effect of temperature on the grain size is small. The primary α-phase grain size increases more rapidly with the increase of temperature at the deformation rate of 0.1 mm/s. The average grain size of α-phase decreases with the increase of the friction factor, and the inhomogeneity of grain size distribution increases.