The stability level and deformation characteristics of slopes are influenced by the mutual effect of various loads. Slopes often experience a coupling application of water level variation and excavation. A series of centrifuge model tests were carried out to observe the response of slopes under different sequences of water level variation and excavation. An image-based measurement system is used to measure the full displacement field of slopes, analyze the failure sequence of tests, and clarify the failure mechanism of slopes under different sequences. The loading sequence significantly influences the deformation and failure characteristics of the slope. It has been proven that slip surfaces form from the bottom to the top of slopes. The safety limit of the slope is greater under the water level variation-excavation sequence than under the opposite sequence. The slope deformation appears in a limited region that expands during the test. The influence mechanism of water level variation is analyzed, and it is found that water level variation increases the deformation in an area near the slope surface under excavation conditions. The failure mechanism of the slope under excavation and water level variation can be illustrated by significant coupling processes of deformation localization and local failure. The inversion of the loading sequence changes the location of deformation localization and thus induces variation in the position of the slip surface.