Abstract: A horizontal beam deflector with a rotating polycylinder mirror used for the situation of high scan frequuency is newly designed.The material and processing technology of the cylinder body are brought forward.The optical character and the scan result of the rotating polycylinder mirror are studied.The dynamic character of the rotating polyclinder-mirror is studied too.The lens to correct the scan light nonlinear deflection by the rotating mirror is studied.As the horizontal beam deflector,the rotating polycylinder-mirror can simplify the structure and decrease the cost of system.The static and dynamic balance is easy to be insured because of the lower rotating speed of polycylinder-mirror,and also resulted in a high rotating precision.The light deflected by the rotating mirror can be corrected by correcting lens,which inccreases the property of system.