In order to find a way to increase the life satisfaction of adults living in the age of COVID-19, factors affecting life satisfaction were analyzed by youth, middle-aged, and elderly generations through the application of Alderfer’s ERG theory. To this end, we analyzed the responses of 1,233 people over the age of 18 using the data of the “Research Survey for the Development of Goyang Citizens’ Happiness Promotion Indicators” surveyed in 2020. The life satisfaction of the three groups was highest among the elderly, followed by the young and middle-aged, but there was no statistical difference. As a result of analyzing the major factors affecting life satisfaction by generation, it was found that the effects of subjective health, social relationships, and leisure satisfaction on life satisfaction for the elderly and middle-aged were significant. In the case of young people, subjective health and social relationship had a significant effect on life satisfaction. And the fear of COVID-19 infection is negatively affecting life satisfaction. It can be seen that the fear of COVID-19 infection has a greater impact on young people than on the elderly and middle-aged. On the other hand, it was found that leisure satisfaction had no significant effect on life satisfaction among young people. Leisure was suggested to be more important in the life of the elderly and middle-aged. Based on these research results, suggestions were made to improve life satisfaction by life cycle in the era of COVID-19.