Abstract: Type QH-200 conveyor-belt nuclear scales is a reliable, on-line device that weighs solids mass flow on continuous conveyor by γ-ray absorption and scattering. The operation principle and measuring method are described. And some factors influencing accuracy of the conveyor belt weighing scales are discussed. The full scale total weight of type QH-200 is 10~6t. The result of calibration in the industrial field shows that the accuracy of QH-200 is better than ±1.0％ for typical belt loading.