This paper presents a novel method for retargeting motions. In this method we consider the whole leg as a length changeable skeleton, through keeping the length proportion and direction of the leg vector before and after retargeting we can accomplish the motion retargeting by scale the root node. Because we transform the constraint of foot position to the constraints of the leg vector's length and direction and adjusting the leg vector is easy, our method need not the complex optimization algorithm. The experimental results show that the method is a real-time method and the characteristic of foot trajectory can be kept after retargeting.