Step framing is an important method to enlarge the covered working area of a traditional array CCD aerial camera. A simple structure step framing aerial camera is presented. By adopting open-loop control of a stepper motor to achieve the scanning process, the camera is especially suited for occasions that the volume and weight is strictly limited.The design of a high-order smooth motion curve of a stepper motor based on versine functions and its implementation on the Digital Signal Processor (DSP) are introduced in detail. The experiment indicates that the control strategy effectively restrains the impulsion and residual vibration and the out-of-step conditions of the stepper motor are avoided. The repetitive positioning accuracy is better than 10”. The system meets the requirements of the step framing camera with simple structure and low cost.