In this paper, we investigate the optimal spectrum leasing and sharing for dynamic spectrum access (DSA) network which actively shares its spectrum resource with a group of secondary users (SUs) for reaping revenue. The DSA aims at maximizing its total charge to the SUs based on their achieved throughput, while taking into account the additional power consumption of the primary user (PU) to overcome the SUs' interference such that quality of service (QoS) of the PU is guaranteed. The interference between the PU and the SUs as well as the interference within the SUs themselves make the spectrum leasing problem strictly nonconvex and thus difficult to solve in general. To tackle with this difficulty, we exploit the decomposition structure of the concerned spectrum leasing problem and propose a layered monotonic optimization approach to solve it efficiently. Numerical results are presented to validate our proposed approach and its computational efficiency.