To design faster and safer printers with scorotron, it should be highly effective in charging of rotating optical photoconductor (OPC). In high speed printings, the time scale of rotation and charging competes and the charging processes goes to transitional. So, we have to understand dynamics of charging processes for effective charging scorotron. But, the dynamics of charging of rotating OPC by scorotron is not well understood. The authors have recently developed a numerical model of the dynamics of charging rotating OPC and ionic wind by positive DC scorotron. The calculation by the model well reproduced the measured electrostatic potential on rotating OPC and velocity of ionic wind in steady state. The authors show how electrostatic potential on rotating OPC and charge density distribution change with time. The authors also show that the charging time scale by the model.