The invention discloses an aviation aluminium alloy U-shaped frame section bar and a preparation method thereof. The aviation aluminium alloy U-shaped frame section bar is prepared from the followingelements in percentage by weight: 5.6-6.5% of Zn, 1.4-2.4% of Cu, less than 0.1% of Mn, 1.8-2.6% of Mg, 0.2-0.25% of Cr, 0.25-0.35% of Fe, equal to or less than 0.1% of Si, less than 0.08% of Ti and the balance of Al. According to the preparation method, through the set alloy composition and the specific preparation technology including extruding, rolling and bending, the aviation aluminium alloyU-shaped frame section bar formed at one time is obtained, on one hand, the tensile strength and yield strength of U-shaped frame section bar are greatly improved, finally, the tensile strength can reach 550-609 MPa, the yield strength can reach 490-546 MPa, the elongation is 7-11%, the planar clearance is equal to or less than 1 mm, the perpendicularity is equal to or less than 1 degree, which are much better than the using standard, and on the other hand, the precision of the U-shaped frame section bar is greatly improved, the prepared U-shaped frame section bar has excellent planar flatnessto ensure stability consistency of quality, can completely meet the using requirement of aviation aluminium alloy section bar, and provides material guarantee for research of a novel spaceflight carrier rocket in China.