In view of the defects such as instability, wrinkling and cross-sectional distortion that were easily produced during push-bending of tubes with long straight section and small bending radius, 5B02 aluminum alloy tubes with the specification of Φ25 mm×1 mm and the bending radius of 1D were formed by internal expansion and cold push-bending process with polyurethane filler, and the internal pressure distribution of polyurethane filler during the push-bending process was studied by finite element simulation. Then, by analyzing reverse thrust, polyurethane filler parameters and internal friction, the internal pressure distribution of polyurethane filler was obtained, and the relationship between internal pressure and defects was determined to realize the controllable internal pressure. The research results show that when the reverse thrust is increased to 13 MPa, the tube is not well formed. When the reverse thrust is reduced to 5 MPa, the internal pressure of supporting elbow is insufficient, resulting in instability and port distortion of elbow. When the hardness of polyurethane filler is insufficient, the cross-sectional distortion of elbow is aggravated. The change of friction coefficient between polyurethane filler and tube affects the internal pressure provided by the polyurethane filler, and when the friction coefficient is small, it leads to insufficient forming and causes instability and wrinkle of tube. Thus, the feasibility of controllable internal pressure push bending is verified by the above study.