The existing research on the temporal heterogeneity across the urban-internal polycentric developments remains insufficient. To fill this research gap, we employed the relative minimum threshold approach to measure the intra-city morphological polycentricity in Chinese prefecture-level cities, 2005-2015, using the 1-km-grid population dataset. The hierarchical-cluster analysis was then adopted to induce the patterns of temporal variations in polycentricity. Finally, the mixed effect model is used to capture the temporal heterogeneity and explore the correlation factors of intra-city polycentricity during the focal period. The results showed that: (1) the multicenter structure of Chinese cities has been basically formed around 2010; (2) five evolution patterns were identified; (3) the urban-internal morphological polycentricity presented significant correlations with the geographic features, demographic characteristics, economic performance, infrastructures, and city size; (4) consistent with the classic urban structure theory, the evolution in urban China exhibited significant temporal variations and conformed to the diffusion-coalescence development pattern. The research findings and corresponding methodologies of the current research can help to advance the understanding of patterns of urban polycentric developments in urban China.