This paper solves stochastic unit commitment problems using multi-cut decomposition algorithm with partial aggregation. The generation unavailability and load uncertainty are both incorporated into the unit commitment formulation, and it is demonstrated by simulations that this method has better performance in economic and reliability perspective than its deterministic counterpart. The modified version of multi-cut algorithm is used to solve this large-scale unit commitment problem. The efficiency of this modified multi-cut algorithm with different levels of aggregation is examined by numerical studies, which show that the computational cost is significantly reduced by the algorithm.