Understanding how the SIMDual-K-c model parameters affecting the evapotranspiration (ET) in a maize field under film mulched drip irrigation is important in improving the model accuracy and applicability, and achieving the precise ET modeling in the film mulched drip irrigation fields. In this study, we used the Extended Fourier Amplitude Sensitivity Test (EFAST) method to conduct a global sensitivity analysis (GSA) of the model parameters based on field observations from 2022 to 2023 in an arid region of the Northwest China. Sensitivity parameters were identified to enhance the efficiency and precision of parameter calibration. The sensitive parameters for soil surface evaporation (E) were the rate of mulch coverage (f(m)), total evaporable water (TEW), and depth of the surface soil layer subject to drying by evaporation (Z(e)). The sensitive parameters for plant transpiration (T) were the mid-growth base crop coefficient (K-cb mid) and end-growth base crop coefficient (K-cb end). Mulching altered E by preventing direct exposure of the soil surface to the air, thereby demonstrating a negative correlation between the f(m) and E. The soil surface became more vulnerable to solar energy and wind speed with the increase in Z(e), consequently increasing E and showed a positive correlation between the Z(e) and E. The greater the TEW, the larger the E became when the surface soil was completely wet, showed a positive correlation between the TEW and E. The K-cb mid had a positive correlation with T, with its impact far exceeding that of the initial-growth base crop coefficient (K-cb ini) and K-cb end. The root mean square error (RMSE) were 48.93 and 57.34 mm, and Nash-Sutcliffe Efficiency (NSE) were 0.78 and 0.73 in 2022 and 2023, respectively. The fitted line for ET estimated by the SIMDual-K-c model in different planting years closely matched the 1:1 line, indicating that the SIMDual-K-c model was able to estimate the ET for the maize fields under film mulched drip irrigation effectively.