The invention relates to a sensor for measuring water content of oil water. The sensor comprises a double-layer nested housing and a pair of wide-band antenna; wherein the double-layer nested housing comprises an external layer shielding housing and an internal layer isolation housing which is coaxially nested in the external layer shielding housing, an interval is arranged between the external layer shielding housing and the internal layer isolation housing and is filled with a water-absorption substance, the wide-band antenna can be symmetrically arranged between the external layer shielding housing and the internal layer isolation housing, and the radiation direction of the wide-band antenna is perpendicular to the antenna. The pollution on the sensor by crude oil is little, compared with a ray method for measuring the water content of a medium, the sensor has the advantages of high security, economical and practical performances, and low cost, compared with a ultrasonic method, the pressure influence on signal transmission is little.