Current safety detection methods for emergency power supply following an earthquake generally ignore the three-phase current asymmetry of the power grid node; nor are node power of the network, branch current, and network loss calculated. This results in low accuracy in node network safety detection. Based on this premise, a power network security detection method for emergency power supply following earthquakes is proposed. According to the operation parameters of the connectivity matrix power network node, the voltage vector of different nodes was obtained using the power flow calculation. The fast-coupled method was used to optimize the calculation speed of the Newton-Raphson method, and node power, branch current, and network loss values were calculated. Based on the constructed safety detection model of the power network node connectivity, the Monte Carlo method was used to accomplish the power network security detection for emergency power supply following an earthquake. The experimental results showed that the proposed method could effectively detect the safety of power network nodes for post-earthquake emergency power supply. When the vibration acceleration was 0.05 gal, 0.20 gal, and 0.80 gal, the safety test results of the experimental objects were high, medium, and extreme, respectively, which was consistent with the actual results, and indicated that the proposed method can also accurately detect the security of the connectivity of power network nodes.