<p>Incremental liquid impact forming (ILIF), a method based on cavity volume change, is proposed to reduce dependence on external high-pressure sources during the T-shaped tube hydroforming process. In this paper, the inner cavity volume was compressed during the feeding process to generate the pressure required for bulging, which enabled the collaborative forming of feeding-compression-pressurization. Then, an iterative simulation method was developed to calculate internal pressure, based on the process characteristics of T-shaped tube ILIF, emphasizing minimal liquid volume and maximum forming pressure. The error between the simulated input pressure and the pressure generated by volume compression during the forming process was controlled within 1%. The reliability of the simulation method was verified by pressure monitoring during forming tests. Finally, forming tests were conducted on an H65 brass T-shaped tube, utilizing the same peak pressure and total feeding volume. The results showed that ILIF led to a greater reduction in wall thickness in the later stages compared to conventional hydroforming.</p>