The invention relates to a device and a method for measuring the stability, belongs to the technical field of soil measurement, and particularly relates to a device and a method for measuring the stability of a strong suspension pulp at the normal temperature. The main principle is that a slurry container is divided into two cone parts, the volumes of the upper part and the lower part are the same, the normal sedimentation of the slurry is not affected, the upper part and the lower part of the container are connected through a union, and after the slurry stands for a set time, the union is slightly screwed, a valve is closed, the upper container and the lower container are communicated, the slurry in the upper-layer container and the slurry in the lower-layer container are respectively poured out from the top part and the bottom part, the weights of the slurries are weighed, and the settleability of the slurry is obtained through the mass difference of the slurry on the upper layer andthe slurry on the lower layer.