Since the traditional contact measuring method leads to the direct contact between the testing equipment and yarns and then causes friction loss， a non-contact measuring method is proposed and a non-contact measuring system for yarn tension based on machine vision is designed. Binocular cameras are used to detect the consumption speed of yarn ends. The yarn’s retraction and unwind speed are regulated. And the yarn tension is kept stable. Compared with the conventional tension control methods， the yarn tension change amplitude of the non-contact yarn tension measurement system based on machine vision，is decreased to only 25% of the original. This method has high accuracy and reliability， and can achieve active control of 3D braided yarn tension. It holds strong application potential.