A method for cooling a steel strip by mist cooling in a cooling installation of a galvannealing furnace configured to perform galvannealing treatment on a hot-dip galvanized steel strip, the method comprising: by mist headers arranged in multiple stages at a cooling-zone preceding stage section provided at the upstream side in a sheet-passing direction and a cooling-zone subsequent stage section provided at the downstream side in the sheet-passing direction with respect to the cooling-zone preceding stage section, jetting mist to the steel strip passing therethrough, by an adjusted cooling installation provided at an upstream side in the sheet-passing direction of the cooling-zone preceding stage section, jetting mist to the steel strip passing through the cooling installation in a manner that an amount of mist jetted to the steel strip passing through the cooling installation is smaller in an edge portion in a width direction of the steel strip than in a center portion; by a mist suction installation provided at least at a downstream side in the sheet-passing direction of the cooling installation, sucking at least part of mist jetted to the steel strip; by a control apparatus, controlling the adjusted cooling installation and the mist suction installation for cooling the steel strip at a sheet-passing speed such that, during a period between start and end of cooling of the steel strip, a temperature of the steel strip is within a film boiling temperature range and a temperature of the edge portion in the width direction of the steel strip is equal to or higher than a temperature of the center portion in at least a range of 2/3 or more from the upstream side in the sheet-passing direction of a total cooling length of the cooling installation, wherein, with respect to an installation length L [m] of the adjusted cooling installation, a speed of the steel strip is set to be equal to or less than an upper limit speed V max [m/s] calculated using a formula (a) below, V max = L × T in − β ′ ∧ m × T in − γ ′ / α ′ × th where T in [°C] denotes a temperature of the center portion of the steel strip at an entrance of the cooling installation, th [m] denotes a thickness of the steel strip, and α', β', γ', and m are constants set according to a hot-dip galvannealing installation. by mist headers arranged in multiple stages at a cooling-zone preceding stage section provided at the upstream side in a sheet-passing direction and a cooling-zone subsequent stage section provided at the downstream side in the sheet-passing direction with respect to the cooling-zone preceding stage section, jetting mist to the steel strip passing therethrough, by an adjusted cooling installation provided at an upstream side in the sheet-passing direction of the cooling-zone preceding stage section, jetting mist to the steel strip passing through the cooling installation in a manner that an amount of mist jetted to the steel strip passing through the cooling installation is smaller in an edge portion in a width direction of the steel strip than in a center portion; by a mist suction installation provided at least at a downstream side in the sheet-passing direction of the cooling installation, sucking at least part of mist jetted to the steel strip; by a control apparatus, controlling the adjusted cooling installation and the mist suction installation for cooling the steel strip at a sheet-passing speed such that, during a period between start and end of cooling of the steel strip, a temperature of the steel strip is within a film boiling temperature range and a temperature of the edge portion in the width direction of the steel strip is equal to or higher than a temperature of the center portion in at least a range of 2/3 or more from the upstream side in the sheet-passing direction of a total cooling length of the cooling installation, wherein, with respect to an installation length L [m] of the adjusted cooling installation, a speed of the steel strip is set to be equal to or less than an upper limit speed V max [m/s] calculated using a formula (a) below, V max = L × T in − β ′ ∧ m × T in − γ ′ / α ′ × th where T in [°C] denotes a temperature of the center portion of the steel strip at an entrance of the cooling installation, th [m] denotes a thickness of the steel strip, and α', β', γ', and m are constants set according to a hot-dip galvannealing installation.