The invention discloses an aluminum alloy semi-trailer longitudinal beam assembly, belonging to the technical field of semi-trailer production. The technical scheme comprises an upper wing plate and alow wing plate, wherein a plurality of webs are intermittently connected between the upper wing plate and the lower wing plate; a plurality of support plates are connected between the upper wing plate and the lower wing plate between adjacent webs; stress dispersion holes are arranged on the webs; and anti-crack edges formed by welding are arranged on the edges of the stress dispersion holes, sothat the lightweight degree and the load bearing performance of the upper wing plate are improved.