The invention relates to a downhole expansion tool for a sleeve. The downhole expansion tool for the sleeve comprises an expansion assembly and a driving device, wherein the expansion assembly is used for expanding the sleeve, and the driving device is used for driving the expansion assembly to carry out expansion operation. According to the downhole expansion tool for the sleeve, when well drilling is carried out, the borehole size can be kept to be constant, constant hole diameter drilling and well completion operation of a whole well are achieved, and the downhole expansion tool for the sleeve is particularly applicable to construction of deep wells, extra-deep wells and complex wells.