Traditional magnetic wall-climbing robot can not meet well the requirements on manoeuvrability, loading ability and self-adaptability on irregular ferromagnetic surface at the same time. A novel magnetic-wheel unit was introduced to solve this problem. The magnetic-wheel unit consists of wheel, permanent-magnet blocks and connecting parts. Its characteristic is that the permanentmagnet block is set symmetrically around the wheel and there is a distance between the block and the surface. There is a stable adsorption force between the unit and the surface, whatever the surface has different curvature radius. A novel wall-climbing robot, comprising of three units, was designed. Finite element analysis results show that the adsorption force varies less than 6%, when the robot is placed on the cylindrical surface with a curvature radius bigger than 1.5 m. the results are better than traditional mechanism.