Large-scale parabolic trough collectors (PTCs) are generally installed in flat, open areas. Their specific costs 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 were deduced between a full-sized model 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. 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, comparing with the other turbulence model, the ke turbulence model has a 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 which can be used to bypass costly numerical simulation and/or wind tunnel testing for the estimation of wind loads on the large-scale PTCs installed in flat, open areas.