The existing anchor cable prestress detection equipments can only be used when the length of the exposed section of the anchor is above 70cm and the anchor cable is not in operation and maintenance period. Most of these devices weigh more than 150 kg， which is too heavy for detectiing the anchor in high and steep slopes. In order to overcome the above problems， a new anchor cable prestress detection equipment HRAD-300 was developed. It can be applied to the prestress detection of in-service anchor with exposed length of 7cm. The measurement error is less than 0.01mm when the displacement range of the detector is 200mm， while the measurement error is ±1%FS when the force range is 300kN. The weight of a single box of the equipment is less than 15kg， and the total weight is less than 40kg. Based on the principle of reverse pull method and the shape of detection curve， the effective anchored prestress algorithm was proposed， and the software is programmed. The indoor test shows that there are no obvious mutation points in the detection curve. The calculated values were basically consistent with the original locked values. The equipment was used to detect the anchor of the unstable slope of Fenghuang rock. The field anchor detection curves has obvious mutation points and steep drops. The anchor cable runs well and keeps on working. The prestress loss of the No.2 anchor cable is more obvious， and the way of compensate and stretch can be taken. Uneven stress exists in the same anchor cable. In conclusion， the HRAD-300 is intelligent and light， which can provide data for the health evaluation of anchorage engineering.