Abstract: In order to research influence of mixing time on yield stress of viscous material, the paper introduced a design scheme of yield stress testing device of viscous material based on vane spindle method and expounded design methods of structure, circuit and rotor and testing method of the device. When the device mixes coal slurry with amount of solid of 57.37% for 240 min at 8 r/min, the maximum fiducial error of the maximum yield stress is 1.25%, the maximum relative error is 5.45% and repeating precision is less than 3%. When the device mixes coal slurry with amount of solid of 60.89% at 8 r/min, the value of yield stress-time curve of the coal slurry increases first and then decreases with obvious peak, and variable speed of yield stress slows down and goes stable after 120 min.