Abstract: In large multi-span greenhouses, the traditional negative pressure fan-pad cooling system suffers from poor uniformity of indoor air temperature and disrupts the integrity of the cultivation area, whereas existing positive pressure ventilation systems using the air-handling corridor exhibit low integration and are difficult to control. To overcome these limitations, this study designs a packaged positive pressure ventilation and cooling system to ensure efficient and high-quality crop production in multi-span greenhouses during warm seasons. The system consists of an equipment room, a combined air conditioning unit with three-sided air intake, ventilation ducts, and a control module. It can be further extended with heat sources and a water recirculating system, enabling integrated greenhouse climate conditioning based on positive pressure ventilation. The air flows during the cooling process are as follows: outdoor air enters the equipment room through outer vents, undergoes evaporative cooling in the air conditioning unit, and is conveyed into the greenhouse via underground ducts, while warm air is exhausted through roof vents. Field tests conducted in Shouguang, Shandong province, revealed that during the peak temperature hours (10:00-16:00) in summer, the system together with the external shading screen maintained the daily mean greenhouse air temperature between 28.4 and 32.5 ℃, which was 0.8 to 3.8 ℃ lower than the outdoor temperature. When the system was in operation, the vapor pressure deficit of the indoor air averaged 0.87-1.33 kPa, and the daily mean relative humidity ranged from 62% to 80%, 17–29 percentage points higher than outdoors. The terminal air outlets, uniformly distributed across the cultivation area, delivered airflow at velocities of 7.7–13.3 m/s, achieving a uniformity (standard deviation) of ±1.9 m/s. Under this supply air condition, horizontal air temperature uniformity inside the greenhouse reached ±0.4 ℃. Vertically, air temperature increased with height, exhibiting a gradient of 0.76 ℃/m, with a 3.1 ℃ difference between the tomato canopy and the greenhouse roof. When combined with the high-pressure fogging system installed inside the greenhouse, a three-dimensional cooling effect was achieved, reducing the vertical temperature gradient to 0.5 ℃/m. The designed specific ventilation rate of the greenhouse for cooling purposes was 0.028 m/s. During the test, the actual ventilation rate and system power consumption were 0.014 m/s and 15.2  W/m², respectively, yielding an average cooling capacity of 144.2 W/m² to the greenhouse, an energy efficiency ratio of 9.5, and an average indoor–outdoor air temperature difference of 2.1 ℃ (08:30–17:30). The overall cooling efficiency reached 95.9%, with the daily average of the water consumption rate for evaporative cooling ranging from 0.033 to 0.065 g/(m²·s). Compared with the negative pressure fan-pad cooling system, the proposed packaged positive pressure ventilation and cooling system requires a lower specific ventilation rate to achieve the same greenhouse cooling amplitude, while exhibiting superior cooling uniformity and efficiency. In comparison with the air-handling corridor based positive pressure ventilation system, it offers a longer air supply distance, though with relatively higher energy consumption. This research provides a novel and high-efficiency mechanical ventilation solution for cooling multi-span greenhouses and designing semi-closed greenhouses.