The main aim of this work is to optimize the operational parameters of using evaporative cooling system such as thickness of pads and air velocity. To achieve that, study the effect of different pad thicknesses (10, 15 and 20 cm) and different air velocities (1.5, 3.0, 4.5 and 6.0 m s^-1) on air temperature, relative humidity, temperature reduction, cooling efficiency and cooling capacity in greenhouse. The obtained results indicated that the hourly temperature of air increased gradually until it reached the peak at 12.00 PM and then decreased during period from 9 AM to 6 PM. Also, the air temperature decreases with increasing pad thickness. The hourly relative humidity of air decreased gradually until it reached the lowest value at 12.00 PM and then increased during period from 9 AM to 6 PM. The temperature reduction increased from 4.0 to 5.9, 6.9 to 8.4, 6.9 to 8.8 and 8.4 to 11.6 °C when the pad thickness increased from 10 to 20 cm, respectively for 1.5, 3.0, 4.5 and 6.0 m s^-1 air velocity. The highest value of temperature reduction was 11.6 °C was found with 20 cm pad thickness and 6.0 m s^-1air velocity. The cooling efficiency increased from 41.2 to 58.8, 55.2 to 67.2, 50.4 to 80.7 and 64.1 to 88.6 % when the pad thickness increased from 10 to 20 cm, respectively for 1.5, 3.0, 4.5 and 6.0 m s^-1 air velocity. The highest value of cooling capacity was 250.1 kW was found with 20 cm pad thickness and 6.0 m s^-1air velocity.