Abstract: The location and morphology of beaches vary constantly due to the influences of natural changes and human activities. In order to accurately assess the evolution process of a beach and further provide a basis both for the design of coastal engineering and for the setting-up of beach erosion protection strategies, a large number of satellite images obtained from 1984 to 2021 are used and sub-pixel technology and methods combining automatic and manual interaction are applied to analyze the spatio-temporal evolution of three typical beaches in Qingdao over the past 40 years, including the identification of the positions of wet/dry line and waterline of the beaches on the studied transect and the positions of mean high- and low-tide lines. The results indicate that human activities such as coastal engineering construction and the beach topography (including headlands, degree of beach closure) are the main factors affecting beach evolution. The Taiping Bay Beach has been in a basic stable state for a long time under the protection of embankments on both sides, where the evolution rate of high tide line was 0—0.1 from 1984 to 2014. For the Fushan Bay Beach, the sand replenishment activity carried out in June 2017 coincides perfectly with a rapidly lifting of the average high tide line in the Fushan Bay after 2017 obtained in this study, with an lifting rate being as high as 0.6—1.8. In addition, the sea level rising has also excerted a certain impact on the evolution of beaches in Qingdao. The Liuqinghe Beach shows that its average high tide line has been moving landward in recent years, indicating an erosion trend with an erosion rate of 0.6—1.1.