Abstract：Microtubules consist of cytoskeleton multifilament proteins and play significant roles in many fundamental biological processes including cell division, cellular transport and motility. Both inside and outside of the cell, microtubules manifest an unique dynamic instability. In this paper, we investigate the dynamic instability of microtubules using a cooperative hydrolysis model. For this model, any GIPtubulin hydrolyzes with a rate depending on the states of its neighbors, we use α to describe the influences of its neighbors. Using a new theoretical method, we calculate the steady state of its neighbors. Using a new theoretical method, we calculate the steady state of this model. The influences of α to the dynamics instability of microtubules are discussed. The results show that α influences the distribution of Tsubunit clearly, and α influences the cap size remarkably, especially when U is small.