Abstract: Reducing chemical fertilizer use while improving its application efficiency is a fundamental requirement for achieving high-quality and green agricultural development. The provision of agricultural machinery services has transformed the allocation and utilization efficiency of agricultural production factors. However, the extent to which these services reduce chemical fertilizer use remains insufficiently understood. Based on a provincial panel data from 2000 to 2024, this study employs a two-way fixed-effects model to empirically examine the impact of agricultural machinery services on chemical fertilizer application intensity and the underlying mechanisms. Results show that: 1) agricultural machinery services significantly reduce chemical fertilizer application intensity, and the relationship between the two is inverted U-shaped. China’s overall level of agricultural machinery service development has surpassed the turning point, indicating that the fertilizer-reducing effect is likely to continue strengthening; 2) heterogeneity analysis indicates that regional variation exists in the chemical fertilizer reduction effect of agricultural machinery services: the low service level stage showed a significant inverted U-shaped feature, and the reduction effect was more obvious in the high service level stage. The reduction effect is more pronounced in plains and economically developed regions but remains relatively limited in mountainous and less-developed areas; and 3) mechanism analysis shows that the specialization of agricultural machinery serves is a key transmission channel for reducing fertilizer use, while the scale of agricultural operations and digital accessibility strengthen the fertilizer-reducing effect. Accordingly, the green orientation of agricultural machinery services should be strengthened by encouraging service providers to shift their focus from scale expansion to environmentally sustainable practices, adopting differentiated measures to promote service specialization and digital empowerment, improving service providers’ precision-fertilization capabilities, and transforming fertilizer application from extensive use toward more precise and efficient practices.