Abstract: Studying the influence mechanism of urban expansion on fertilizer input is of great significance for standardizing fertilizer application and management, and rationally regulating the process of urbanization. This research uses the five-phase of socio-economic development data and land use panel data of the core region of the Yangtze River Delta, combining fixed effect model and path analysis to explore the direct and indirect effects of urban expansion on fertilizer input. It is found that: (1) urban expansion does not has a significant direct effect on fertilizer input, but it will  indirect increase the intensity of fertilizer application; (2) Urban expansion will lead to the instability of farmland property rights, the reduction of agricultural labor input, and the increase of farmers' income levels, thereby increasing the intensity of fertilizer application；but at the same time reducing the fragmentation of farmland to inhibit the intensity of fertilizer application; (3) The effect of property rights instability and labor play the most important role, while the effect of income level and fragmentation of cultivated land is relatively weak. Thus, taking into account the effects of instability of farmland property rights, the decrease in agricultural labor input and the increase in farmers' incomes on fertilizer input, this paper aims to put forward policy recommendations to strengthen construction land management and control, stabilize farmland property rights, popularize environmentally friendly agricultural technologies and promote comprehensive land consolidation.