A rotary adjusting mechanism is provided that includes a crank sliding block mechanism assembly and a driving motor assembly. The crank sliding block mechanism assembly includes a machine frame, a crank and a connection rod. The driving motor assembly is mounted on the machine frame and drives the crank. The crank is rotatably mounted on the machine frame by a first connection shaft. The connection rod used for mounting a screen is rotatably mounted on the crank by a second connection shaft. The machine frame has a guide groove. A sliding block linearly moves along a path defined by the guide groove. The connection rod is rotatably mounted on the sliding block by a third connection shaft. The first, second and third connection shafts extending in the z direction. The resulting device is simple in structure, small in the number of dimension chain control links, and high in mechanism reliability.