By aggregating massive distributed resources in distribution networks, virtual power plants (VPPs) are formed to create flexible portfolios used in electricity market regulation and grid dispatching, thereby addressing power supply-demand imbalances. However, in existing VPP energy management strategies, the effective consideration of distribution network operational security remains a key challenge. To achieve both efficient coordination of distributed resources within VPPs and secure operation of distribution networks, the distribution network security-region theory is adopted, whereby a dynamic distributed energy management strategy is constructed. A security-region model is first established based on the power-flow topology, and a decentralized scheduling framework is then designed for internal VPP resources using a consensus algorithm. By introducing a security-consensus variable defined by the security-region boundary function, economic and security requirements are jointly satisfied, enabling distributed energy management under network security constraints. Case studies show that the security of distribution network power flows is effectively ensured, and internal VPP resources are regulated rapidly, accurately, and dynamically.