Software-Defined Networking (SDN) brings great opportunities to improve network performance. However, due to budget constraints and technique limitations, Internet Service Providers (ISPs) can upgrade only a limited number of conventional switches to SDN switches in real backbone networks at one time. In this paper, we propose one heuristic scheme for deploying SDN switches in hybrid SDNs. Our scheme works for two different cases: (1) maximizing the network control ability with a given upgrading budget constraint, and (2) minimizing the upgrading cost to achieve the best network control ability. We evaluate our scheme in real topologies. We evaluate our scheme in real topologies. The results show that our scheme can achieve 95% of flows controlled with only 10% upgrading cost.