The traditional security situation assessment mainly focuses on the small scale network system, which has neglected the risk correlation among network nodes. In view of the complex network structure in the energy Internet, a quantitative assessment for multi-node network security situation based on threat propagation is proposed. This method firstly gives concept and definition of network nodes in energy Internet, and models the energy Internet network structure by using graph theory; secondly, quantitative method is proposed based on threat propagation probability to calculate the node security situation, also a multi-node weighting method called LR-NodeRank is put forward to evaluate fusion network security situation. Finally, a security situation improvement based on the simplest threat graph is proposed to calculate the network border needed to reinforce. Experimental results show that the proposed method can accurately assess the security situation of multi-node network, and can also effectively carry out the border connections.