The invention discloses an assembled portable ladder for a building construction layer, which comprises a pedal skeleton, a pedal, a side beam and a cross beam; the pedal skeleton, the pedal, the side beam and the cross beam form a stairs unit which can be connected end to end by at least two stages; the lower part, the middle part and the upper part of the side beam of the stairs unit are respectively provided with a lower connector, a middle connector and an upper connector; and the middle connector and the upper connector are provided with holes for installing bolts. The side beam is arranged between the lower connector and the middle connector or/and between the middle connector and the upper connector, and is provided with a movable connector with adjustable position; and the movableconnector is provided with the hole for installing bolts. The bolts are in L-shaped structure. Bolts are adopted for connection when the stairs units are connected end to end. The assembled portable ladder for the building construction layer has simple and reasonable structure, is convenient to be disassembled and assembled, and is applicable to the cast stairs site of the construction industry.