The rapid adoption of drone for Agro-chemical sprayings, commonly referred to as agricultural drones, has considerably changed precision agriculture by supporting site-specific, timely, and resource-efficient agro-chemical spraying. Conventional ground-based spraying methods are often considered by undue chemical usage, non-uniform application, soil compaction, and increased health risks to operators. In response to these boundaries, drone-based spraying systems have arose as a viable substitute capable of improving application accuracy, operational efficiency, and environmental safety. This paper presents a broad literature-based review aiming on the engineering design of agricultural spraying drones, with particular importance on achieving high spraying efficiency and sustainable field operation. Core design areas examined include airframe configuration, propulsion system selection, payload–endurance trade-offs, spray mechanism design, flight control architectures, and sensor-driven intelligence. The review blends recent advances in drone aerodynamics, fluid dynamics of spray droplets, energy management, and autonomous navigation as they relate to agro-chemical application performance. Measurable performance indicators reported in the literature—such as spray deposition uniformity, droplet size distribution, effective swath width, chemical utilization efficiency, energy consumption, and operational productivity—are systematically explored and compared. The impact of rotor-induced airflow on spray drift and deposition accuracy is also examined as a critical factor affecting field performance. Likewise, this study enhances the research aims and objectives associated with efficient agro-chemical spraying drones, identifies unresolved engineering challenges including limited flight endurance, payload constraints, and lack of standardized evaluation frameworks, and highlights future research directions required for accessible and environmentally liable deployment. The manuscript is tight and formatted to meet international journal standards and is intended to support researchers, engineers, and policymakers involved in advancing drone-based agro-chemical spraying technologies.