Abstract: Abstract: In order to estimate the transpiration of greenhouse cucumber and evaporation beneath the canopy in greenhouses, in this study, we modified basic crop coefficient (Kcb) as well as soil evaporation coefficient (Ke) based on the Modified Dual Crop Coefficient model recommended by FAO-56 by applying measured meteorological data, leaf area index (LAI) and soil moisture data in a greenhouse. The greenhouse reference crop evapotranspiration (ET0) was determined by FAO-56 modified Penman-Monteith (P-M) model. Hence, the greenhouse evapotranspiration (ETc) and transpiration (Tr) were estimated. A field experiment was conducted from March to July (spring-summer) and August to November (autumn-winter) in 2017. By measuring the growth status of cucumber plants in different planting seasons (spring-summer, autumn-winter) in a Venlo-type greenhouse and measuring the ETc and Tr of cucumber by lysimeter and stem flow meter, the Modified Dual Crop Coefficient model predictions were validated. The results showed that the ETc and Tr calculated by the Modified Dual Crop Coefficient model were in good agreements with the measured values. The measured and estimated values of ETc during the whole growing period of greenhouse cucumber in spring-summer were 2.94 and 3.05 mm/d, and the measured and estimated values of ETc during the whole growth period of greenhouse cucumber in autumn-winter were 2.76 and 2.53 mm/d, respectively. The coefficient of determination (R2), the root mean square error (RMSE), and the model efficiency coefficient (Ens) of the Modified Dual Crop Coefficient model in predicting spring-summer cucumber ETc were 0.95, 0.41 mm/d and 0.93, respectively, while the results of error analysis of predicting autumn -winter ETc were 0.91 (R2), 0.48mm/d (RMSE), and 0.90 (Ens). Based on the modification of Dual Crop Coefficient model，the basal crop coefficient of each growing stage of cucumber for spring-summer season were adjusted as 0.17－0.25 (the initial season stage), 1.05 - 1.10 (the middle season stage), 0.33 - 0.68(the late season stage), and the corresponding values for autumn-winter season were adjusted as 0.14 - 0.36 (for the initial season stage), 0.99 - 1.16 (the middle season stage), 0.45 - 0.71 (the late season stage). The measured and estimated daily Tr values by the Modified Dual Crop Coefficient model for spring -summer season were 2.19 and 2.37 mm/d, and the measured and estimated average daily Tr values by the Modified Dual Crop Coefficient model for autumn-winter season were 1.34 and 1.43 mm/d, respectively. Based on the result of estimation, the ratio of average daily Tr to ETc was the highest in the middle season stage with the values of 84.36% (spring-summer season) and 84.79% (autumn-winter season), respectively. The ratio of average daily Tr to ETc was the lowest in the initial season stage with the values of 28.98% (spring-summer season) and 17.64% (autumn-winter season). During the whole growing period, the ratio of average daily Tr to ETc for spring-summer and autumn-winter seasons were 64.62% and 68.59%, respectively. Therefore, the Modified Dual Crop Coefficient model can accurately estimate the Tr of greenhouse cucumber and evaporation beneath the canopy in greenhouses. The study results not only provide the theoretical basis for formulating accurate greenhouse cucumber irrigation system, but also have important significance for controlling greenhouse environment and reducing invalid soil evaporation in greenhouses.