The invention discloses a device for ensuring horizontal spacing of reinforcing steel bars. The device comprises a moulding bed, wherein one side of the moulding bed is provided with a reinforcing steel bar spacing regulating mechanism; the reinforcing steel bar spacing regulating mechanism comprises a transmission part and a reinforcing steel bar supporting part; the transmission part comprises a dowel bar and a transmission plate which can do vertical movement under the driving of the dowel bar; the reinforcing steel bar supporting part comprises a plurality of supporting arms which are symmetrically distributed along the center line of the transmission plate; the supporting arms are rotatably connected with the moulding bed; the supporting arms are mutually engaged with the transmission plate and can rotate under the driving of the transmission plate. The invention further discloses a use method of the device for ensuring horizontal spacing of reinforcing steel bars; the method comprises the device for ensuring horizontal spacing of reinforcing steel bars and installation and use steps of the device. The device is simple in structure, convenient to operate and low in manufacturing cost; the device can meet requirements of different horizontal spacing of the reinforcing steel bars by rotating pull rod bolts and adjusting the positions of limit pins.