Abstract: A shift-register unit, a grid driving circuit and a displaying device, which relates to the technical field of displaying. In the present disclosure, the oxide-semiconductor layers of the oxide thin-film transistors may be delimited into regions according to the total channel widths and the channel lengths required by the oxide thin-film transistors in the shift-register unit, wherein the sum of the widths of the independent semiconductor branches obtained by the delimitation is equal to the required total channel width. Accordingly, one oxide thin-film transistor can realize the required total channel width by using the one or more semiconductor branches, to ensure the normal operation of the oxide thin-film transistor, whereby the oxide-semiconductor layers of the different oxide thin-film transistors can be configured differently, to realize the purpose of reducing the border frame of the displaying device.