The invention discloses a construction method of large-span post-tensioned prestressed longitudinal and transverse frame beams, which comprises the steps of erecting a supporting body, producing a template, arranging a base template and a unilateral template, rolling longitudinal main reinforcements, installing a corrugated tube, rolling hoop reinforcements, embedding utility pipelines, mounting prestressing steel wires, mounting an anchor backing plate, closing a lateral templates, filling concrete grouts, pretensioning and grouting pore canals; in the pretensioning, the prestressing tendons of beams are stretched according to the following steps: (1) firstly, the frame beams at the top layer are stretched and then frame beams at the following layers are stretched; (2) the short spans of the longitudinal and transverse frame beams at the same layer are stretched first, and then the long spans thereof are stretched; (3) the upper prestressing tendon of a building unit is stretched first, and then the lower prestressing tendon thereof are stretched; and the left line and the right line of prestressing tendons are stretched symmetrically and separately. The construction method adopts a stretching order from the upper layer to the lower layer and can construct the prestressed frame beams in accordance with an ordinary reinforced concrete structure layer by layer, thereby being capable of reducing the influence of concrete curing on the construction period and accelerating work progress.