A sizing device for a packaging binding strap for a steel coil structurally comprises a concave support, a sizing groove and sizing baffles. The concave support comprises a base and two side plates fixedly connected with the base, scales are arranged on the upper surface of a sizing groove, sizing baffle sliding channels are formed in the two sides of the sizing groove, a plurality of clamping grooves are formed in the sizing baffle sliding channels, and the sizing baffles are matched with the clamping grooves in the sizing baffle sliding channels. Two sliding wheels are symmetrically arranged at the lower portions of the concave support, and supporting devices are arranged on the outer sides of the two side plates on the concave support. Compared with the prior art, the sizing device for the packaging binding strap of the steel coil has the advantages of being reasonable in design, safe, reliable, favorable for operation and maintenance personnel to and quickly carry out sizing and reduce the waste of the packaging binding strap of the steel coil capable of saving the production cost and improving the labor efficiency and the like.