Disclosed are an inter-network shared frequency spectrum optimization system and method. In the optimization method, a frequency spectrum resource allocated to a first network in a shared frequency spectrum pool comprises a frequency spectrum resource occupied by an OPEN mode base station in a first cell cluster, and a frequency spectrum resource allocated to a second network in the shared frequency spectrum pool comprises a frequency spectrum resource occupied by an OPEN mode base station in a second cell cluster, wherein the frequency spectrum resource occupied by each OPEN mode base station in the first cell cluster and the frequency spectrum resource occupied by each OPEN mode base station in the second cell cluster have the same size. The present invention improves the frequency spectrum efficiency and the base station service quality are improved.