Abstract: A review on the basic characters, influence factors and evolution law of the metal solid phase transformation during hot forming was presented by taking titanium alloy TC4 as an example and the causal chain of the process parameters, phase transformation, microstructure and mechanical behaviors were discussed. It is pointed out that the traditional theory of phase transformation does not include the influence of plastic deformation on phase transformation, and could not be applied for analysis of microstructure evolution and mechanical behaviors of the work piece during hot plastic forming. The experimental results on TC4 alloy phase transformation during hot deformation provided here show the significant influences of hot plastic deformation on phase transformation. An increase in strain rate may hinder phase transformation, and an increase in strain may promote phase transformation.