The invention belongs to the technical field of high-strength aluminum alloy machining, and relates to a postweld heat treatment technology of a high-strength aluminum alloy welding joint. Two-stage solution treatment is carried out on a TIG welding joint of an Al-Zn-Mg-Cu alloy hot-rolled plate, a first-stage solution system is 470 DEG C/90 min, a second-stage solution system is 500 DEG C/20 min, and quenching is carried out in room-temperature water after solution. Through two-stage solution treatment and quenching treatment, a welding line and an original thick primary phase in a base material are basically re-dissolved in a base body, and strengthening caused by re-dissolution of alloy elements of the base material and softening caused by recrystallization are basically balanced. Then artificial aging being 120 DEG C/24 h is carried out, and the strength of the joint can be 621.6 MPa. Compared with the strength, being 589.2 MPa, of a traditional joint obtained through 470 DEG C/2 h solution and 120 DEG C/24 h artificial aging treatment, the remarkable improving effect is achieved.