The invention discloses a roller and a rolling system with variable degree of convexity and a rolling technology with variable degree of convexity, the core point is that the degree of convexity of the roller can be adjusted in subsections. The invention adopts an inlet branch and a plurality of let-off pipes to perform cooling in subsections for the roller, performs on-line measurement for the thickness of a rolling plate through a laser thickness tester, and transfers the measuring data to a computer; the computer system performs comparison processing for the measuring data according to a mathematic model; for a section which does not conform a set profile shape, an execution command is sent to an execution mechanism; a flow metering valve is adjusted to change the temperature of cooling water in the section; the diameter of the roller is partially changed by utilizing the principle of expansion caused by heat and contraction caused by cold of metal so as to achieve the purpose for adjusting and controlling the profile shape. The technology can realize the automatic control for the uniformity of the thickness of the rolling plate, the adjusting and controlling range of is 0-0.1 mm, and the adjusting and controlling precision is plus or minus 0.001 mm.