The invention discloses an erecting method of a large suspension bridge all-weld steel truss stiffening beam. The method comprises the following steps that S1, N balance weights are provided, the weight of the balance weights is recorded as G, and G is larger than or equal to 0 and smaller than the secondary dead load F/N; S2, a stiffening beam segment to be erected is lifted to a main cable, an upper chord of the stiffening beam segment to be erected is connected to an upper chord of an erected stiffening beam segment adjacent to the stiffening beam segment to be erected through an upper chord temporary connecting part; S3, the balance weights are applied to the stiffening beam segment to be erected, and erecting of the stiffening beam segment to be erected is finished; S4, the steps of S2 and S3 are repeated until a line type of a bridge structure formed by the erected stiffening beam segment is a bridge line type; S5, lower chords of two adjacent erected stiffening beam segments areconnected through a lower chord temporary connecting part; and S6, the steps from S2 to S5 are repeated, erecting of all stiffening beam segments is finished, and the stiffening beam is formed. The erecting method cannot affect the length of the stiffening beam, shutdown is not needed, and the inner stress of the stiffening beam is not increased.