A knee-supporting assembly has a supporting device and two belt frames. The supporting device has a securing board assembly, two wheels, a driving axle, an operating member, a transmission assembly, and a pushing member. The wheels are mounted rotatably on the securing board assembly. The driving axle is connected eccentrically with the two wheels. The operating member is connected securely to the driving axle. The transmission assembly is connected with and driven by the driving axle to be reciprocatively moveable relative to the securing board assembly and has a first end connected with the driving axle and a second end. The pushing member is connected with the second end of the transmission assembly. The belt frames are connected respectively with two ends of the securing board assembly.
