Large-scale parabolic trough collectors (PTCs) are generally installed in flat, open areas. Their specific costs ($/m2) are dependent on wind load-based structural design factors. To help estimate these wind loads, validated numerical simulations were used to develop similarity relations for large-scale PTCs. First, similarity relations of wind pressure, force, and lift/drag coefficients were deduced between a full-sized model (FM) and a scaled-down experimental similarity model. Second, the wind loads on the similarity model were simulated with a computational model to analyze the pressure distributions and aerodynamic performance under different wind speeds and pitch angles. Third, the computational method was extended to compute wind loads on a LS-2 collector (a commercial-scale PTC designed by LUZ International Ltd). The numerical results had a close agreement with the experiment results, on the whole, achieving a mean relative error in the drag coefficients of 5.1%, 3.8% in the lift coefficients and 5.0% in the moment coefficients, which indicated that the simulation model was valid. Further, compared with the shear stress transport model for the atmospheric boundary layer (ABL) along with large eddy simulations for the ABL, the k–ɛ turbulence model has better accuracy. Finally, practical similarity equations were proposed which can be used to estimate the wind loads on a range of PTC designs in a wide range of conditions. The mean relative error of these practical similarity equations was found to be within 12.0%. Overall, this study reports a validated set of similarity equations that can be used to bypass costly numerical simulation and/or wind tunnel testing for the estimation of wind loads on the large-scale PTCs (e.g., the EuroTrough) installed in flat, open areas.