Abstract: Anchor is common and important material for reinforcement and support of underground coal mine roadway. If the length of the anchor is not up to the design requirements, it has a great influence on the anchorage quality. Based on the principle that electromagnetic wave can form electric standing wave in the transmission process, we carry out the nondestructive measurement of bolt length, and it can achieve the purpose of rapid, accurate, simple and is suitable for large-scale measurement of anchor length. The design of measuring circuit is introduced.