An isothermal carbon monoxide (CO) shift reactor having high CO conversion and the process technology comprises the outside pressure vessel; the catalyst unit; upper and lower tube sheets welded with water tubes and bottom tee joints; the said outside pressure vessel has seal heads at the upper and lower ends; the said vessel has a water chamber and a steam chamber at the upper section. The catalyst unit comprises the upper catalyst bed with water tubes. There is a central pipe that is located in the said vessel, of which the upper end is located in the upper catalyst bed while the lower end is located in the lower catalyst bed; the said bottom tee joint has an inlet for feed gas, outlet for reacted shift gas and inlet for steam-water mixture; the said central pipe is installed with spray nozzle for steam-water mixture; the said reactor is applicable for process technologies for feed and effluent gas having different CO contents. Low temperature, high CO feed content, high shift conversion and low system pressure drop are direct results of this disclosure.