Energy security is a critical component of national security and a prerequisite for the green and low-carbon transition of the energy system. The concept of energy security has broadened from a traditional focus on fossil fuel supply to include the stable supply and sustainable utilization of energy resources. This study constructs a new energy security assessment framework targeting green and low-carbon transition, analyzing the evolution of energy security in 18 countries worldwide. The findings are as follows: (1) Within a diversified evaluation system aligned with green and low-carbon objectives, energy security has significantly improved in countries with limited oil and gas resources, such as the United Kingdom, Japan, and China. Conversely, the dominant position of countries like the United Arab Emirates and Russia in the international energy market has been reduced. Continued development in renewable energy will reinforce this trend. (2) A strong positive correlation exists between energy security and sustainable development levels in the context of a green and low-carbon transition. Countries with higher sustainability levels have greater advantages in the energy transition process. (3) Sensitivity analysis reveals that although fossil fuel supply remains a key factor in energy security, the importance of diversified supply and sustainable utilization has significantly increased. Therefore, it is recommended that China seize the transition opportunity by leveraging China's resource advantages in renewable energy, enhancing the energy governance system, and focusing on sustainable development. These actions will improve energy security and support China in increasing its influence and proactivity in the international energy market.