This research examines the spatio-temporal distribution of population in an urban environment and its relationship with urban functions using an unprecedented high-resolution and broad-coverage-crowd LBS dataset from Tencent, one of the biggest Internet companies in China. By examining the distribution of the population during different time periods, different urban morphologies are observed. The analysis of the spatio-temporal population distribution based on temporal entropy indicates that population distributions of employment, commercial, and scenic areas have larger temporal fluctuations than those in residential and mixed-use areas. As for the Spearman correlation coefficient between urban functions and temporal population distribution based on 300 × 300-m grids, it is then measured to uncover the underlying reason for this spatio-temporal distribution of population. The result demonstrates that as urban functions become more mixed, the temporal distribution of the population becomes more even. At a local scale, temporal population distribution in key areas shows that the location of people in a certain place is in accordance with human behavior. The population in employment-dominated areas shows large fluctuations on weekdays but is relatively evenly distributed on weekends. The population in commercial areas only peaks for several hours on both weekdays and weekends. Comparatively, mixed areas and large-scale residential communities accommodate a stable number of people at all times.