Incremental sheet metal forming process is considered as one of methods which able manufacturer to produce parts without dedicated die in low and rapid prototype production, and many researches have been done to improve it. Using of ultrasonic vibration is one of the modern approaches in forming processes which reduce friction and forming force. The purpose of this study is to investigate the effect of ultrasonic vibration applied to the tool in single point incremental sheet metal forming process. For this, first theory of single point incremental forming has been studied; its principle has been investigated and analytical relations have been modified then analytical relations in the case of applying ultrasonic are derived from those. To practical evaluation of applying ultrasonic to this process a set can be installed to the head of CNC milling machine is designed and manufactured. According to results of analytic compared to experimental results a reasonable approximation of forming force variation in normal single point incremental forming process and applying ultrasonic can be offered. Based on tests results forming force in applying ultrasonic compare to normal mode reduces between 33 to 63.5 percent depend on test circumstances.