Crucial to regional integration and sustainability of urban agglomeration, coordination between urban land expansion and population growth caused by rapid urbanization has drawn increasing attention. Though the population-land relationship has been widely explored, few studies have investigated the internal mechanism from an allometric growth perspective. This study aims to reveal spatiotemporal evolution and influencing factors of population-land coordination in 26 central cities of Yangtze River Delta (YRD) from 1989 to 2018, via incorporating the coupling coordination model, super-slack-based measure model (Super-SBM), and spatial Durbin model with fixed effects. The results indicated that: 1) the pace of land expansion significantly exceeds population growth, and great distinction of allometric growth within regional cities is observed; 2) population-land interaction is still located in the low coordination stage, and its productivity efficiency sees a slight fall with fluctuation; 3) urban land exploitation, population agglomeration and productivity efficiency have significant positive effects on population-land coordination. Finally, several recommendations are proposed, involving targeted urban land supply for different cities, trans-administrative regional land and industrial planning. This study provides some insights into the sustainable population-land relationship.