Considering the limited storage, computing, and communication resources of smart terminals of the power Internet of Things, most of the existing operation management algorithms focus on reducing power consumption of nodes, which limits the security and anti-capture performance of terminals. For ensuring the performance of terminal nodes in the power Internet of Things, while improving the ability to resist physical capture attack, a lightweight key management scheme is proposed. Firstly, the central control area is increased through the deployment of concentrator nodes, forming a new two-tier grid deployment model. Then based on the new structure, a two-stage key information distribution algorithm is proposed. In each stage, the security threshold of the Blom matrix space is set according to the number of nodes in each sub-area, and greatly improves the connectivity and anti-capture performance of the cyber network. The simulation proves that when the proportion of captured terminals is 5.5%, the failure probability of communication link in the proposed scheme can be reduced by 63% and 68%, respectively, compared with those of the t-UKP scheme and the SPECC scheme.