Greenhouse is one of the methods for increasing water profitability. Soil-less cultivation is of effective factors in increasing efficiency and performance improvement of crops. One of the most essential demands of soil-less cultivation systems is to determine the proper cultivation medium and nutrition solution volume. The most important parameter in crop irrigation management especially for greenhouse crops, is the consumptive water. The objective of this study is to determine the consumptive water of cucumber under the effect of medium type and furthermore, to present an experimental equation for determining cucumber’s consumptive water under greenhouse conditions. The experimental samples for the three medium types include coco-peat + perlite (50%, 50%), coco-peat (100%) and perlite (100%). The experimental samples were cultivated in a microlysimeter in the soil-less cultivation greenhouse located in Isfahan University of Technology. The experiments were carried out by a completely randomized experimental design with four repetitions. In order to determine the crops consumptive water, the soil moisture balance method was used. This method calculates cucumber consumptive water from the differential value between the consumed water and the water drained out of the microlysimeters. An automatic drip irrigation system was applied to accurately manage the irrigation. The irrigation system worked averagely five times a day. The drained water from microlysimeters was measured daily at a specific time and to remove evaporation from the drain below the microlysimeter, the evaporation value was read daily from the free water surface. The weight method was used in order to investigate the moisture balance of the mediums. The results showed that the total cucumber evapotrairation during the 3.5-month growth period for coco-peat + perlite, coco-peat and perlite mediums were read 682.57 (42.66), 572.72 (35.16), 202.82 (12.47) mm (liter), respectively. The average greenhouse temperature during the experiments was 19? C. The maximum cucumber crop height was 148 cm, the bush maximum wet weight was 325.7 g and the maximum crop weight was 3150 g which belonged to the coco-peat + perlite medium. In this study, coco-peat + perlite medium was introduced as the best cultivation medium. The relative humidity and growing degree-days data in greenhouse as well as crop height and consumptive water values were used in the SAS Software to model the water demand procedure. The results showed that the best proposed model for the coco-peat + perlite medium was an exponential no-linear regression model based on growing degree-days, days after cultivation and crop height parameters (NRMSE=14% , R 2 =0.98). For the coco-peat medium, an exponential no-linear regression model based on crop height and daily relative humidity parameters (NRMSE=25%, R 2 =0.91) was reported as the best model for determining water demand. The non-linear regression equation accuracy for determining the water demand was obtained desirably in coco-peat + perlite (R 2 =0.95) and coco-peat mediums (R 2 =0.94). According to the current findings, regression models can be used to determine the crops’ consumptive water in greenhouse environments. Keywords: Greenhouse, Soil-less Cultivation, Water Demand, Coco-peat, Perlite, Cucumber.