With increasing urbanization, the compact use of urban land has attracted increasing attention. The mixing degree of urban land use is an important way to realize intensive and efficient land use. In this study, three types of geographic spatiotemporal data, namely, point of interest (POI) data, taxi GPS data, and mobile phone signaling data, were used to identify and analyze the spatiotemporal differentiation characteristics of the functional mixing degree of urban land use in Zhuhai, China. We used correlation and regression analyses to demonstrate the rationality of using the three types of geographic spatiotemporal data in combination to evaluate the degree of functional mixing. We showed that the results obtained using the three types of geographic spatiotemporal data have different emphases, and their combined use can improve the accuracy of research results. On the whole, the functional mixing degree of land use in the study area was generally low and the spatial distribution varied, gradually decreasing away from the center of the old central city in the east of Zhuhai City to the central city in the west of Doumen District.