This paper describes the inlet prerotation flow of a cross-flow fan and the control. To begin with, the cause of generation of inlet prerotation flow of the cross-flow fan is investigated. Next, it is examined that the prerotation is controlled by the inlet guide vane. As the result, following fact became clear. (1)The prerotation is being generated by drawing in the inlet flow for eccentric vortex of the rotor inside, and therefore, the inlet velocity becomes non-uniform in the circumferential direction. (2)The cross-flow fan becomes a high-efficient and high pressure by controlling the prerotation using the inlet guide vane.