As COVID-19 sweeps through the whole world, human activities have been changed significantly. Under such circumstances, the electricity sector is deeply affected and faced with great challenges. This paper provides a comprehensive review of the impacts that the pandemic has caused on the electricity sector. Electricity demand has dropped sharply as governments around the world executed lockdown restrictions, while the load composition and daily load profile have also changed. The share of renewable generation has increased against the decline of the total electricity generation. Changed power balance situation and increased uncertainty of demand have posed higher pressure on system operators, along with voltage violation issue and challenges for system maintenance and management. The electricity market is also substantially influenced, while long-term investment in clean energy is expected to be stable. The externality such as emission reduction is also discussed.