The forming limitation and the wall thickness distribution are two main parameters for estimating the forming quality of T-shaped tube. In this paper, the effects of three key factors on the forming limitation and the wall thickness distribution are investigated, which are punch front distance l1, reverse height h1 and matching relationship between rubber hardness and axial feed Δl. A new position-limited back pressure mechanism is proposed which is made up of rigid position-limited lever, flexible back pressure medium and rigid spacer. The simulations and experiments are carried out. Both results show the thinning rate of the wall thickness decreases first and then increases and the thickening rate decreases gradually with the increase of l1. The branch reaches the highest with the l1 of 5mm under the requirements of thinning rate and thickening rate. With the increase of reverse height h1, the bigger h1 is beneficial to the wall thickness thinning suppress at the top of branch, the highest branch was formed when h1 is 7mm. When Δl is fixed, the rubber hardness has a great influence on the forming defects, higher rubber hardness causes the top of branch to rupture and lower causes the wall to wrinkle. When rubber hardness is fixed, the thickening rate decreases with the increase of Δl. The best forming limitation and thickness distribution are achieved with the punch front distance l1 of 5mm, the reverse height h1 of 7mm, the rubber hardness of 70HA and the axial feed Δl of 24mm.