Modeling dynamics of complex geographical phenomena is of lots of difficulties in current GIS system. In this paper, Spacetime algebra, a powerful algebra system in expression and analysis of the unified spacetime, is introduced in modeling the dynamics of geographical objects. The basic structure of spacetime algebra and its design schemes are discussed. Case application with satellite altimetry data is also presented. Result suggests that temporal and spatial evolution characteristics of Equatorial Pacific sea level can be extracted by changing the rotation angle and boost ratio. The constructed spatial and temporal projection and statistical parameters suggest that our solution can compare well with ENSO event, which suggests that spacetime algebra can be seen as a powerful tool and a potential way of modeling dynamic changes in GIS.