Conventional large-scale ground sprayers may hardly be deployed in hilly orchards due to the restriction of geo-characteristics, so that manual spray has to be a general approach for plant protection, which results in high labour intensity, low operational efficiency and severe chemical waste. A small self-propelled target-following sprayer for hilly orchards was proposed, which can work together with plant protection UAV. Two coupled nozzles were adopted for the target-following spray mechanism, and the ranges of their spray angle and height were calculated based on the developed physical motion model of droplets. Meanwhile, the method of target detection and tracking and the method of autonomous navigation were integrated into the proposed sprayer to realise autonomous operation. The verification experiment was performed in the apple orchard of Fuyu Forest Fruit Company in Hebei Province, and the results showed that the average coefficient of variation of droplet number deposited on the frontal surfaces of the leaves at different heights of canopies was 34.22%, while that at different sampling points at the same height was 34.56%. Compared with non-target spraying, the target-following spraying could effectively improve the uniformity of droplet distribution on the frontal surfaces of leaves both at different heights and at different internal and external positions of canopies. Besides, water consumption, ground loss and post-canopy drift loss could be reduced by 26.70%, 84.93% and 53.50%, respectively, which indicated that the proposed method can be a technical reference for the development and improvement of hilly orchard sprayers.