The usage of UAV as a pesticide application technology is becoming a common practice in Southeast Asia, with a substantial proportion of agricultural areas currently being treated using this method. To date, more than 169 different UAV designs and configurations have been developed to meet such demand. Each UAV design and configuration have its own unique aerodynamic effects that may have an impact on the resulted spray droplet characteristics and distributions. Therefore, it is crucial to determine both the downwash airflow and spray patterns, and also the effective spraying application parameters for the UAV. This research outlines the development of an indoor test facility and its standardised test procedure for evaluating the downwash airflow and spraying performance of any UAV model used in agricultural applications. The test facility was designed to imitate the UAV in the actual field spraying operation. The developed test facility is 23 m long and has been designed to mount the UAV at up to 100 kg, at three spray heights (1.5 m, 2.5 m and 3.5 m) and operating at a maximum travel speed of 10 m/s. The 6x6 m sampling platform structure for pressure sensors and water-sensitive paper was built under the rail support structure to measure and collect data for the spraying distributions and downwash pressure profiles. With an indoor UAV test facility, recurring experiments based on the same standard protocols could be made available, prospecting improved UAV spraying efficiency and proper recommendations on UAV flying requirements to achieve an efficient agricultural chemical spraying operation.