The windmill generates power by extracting part of the kinetic energy of the wind, and it was aimed to satisfy the basic needs on XVIII and XIX century in Southern Spain. Wind power has been used as long as humans have put sails into the wind. For more than two millenniums wind-powered machines have had ground grain and pumped water. After designing mecanism the simulation with Computational Fluid Dynamics (CFD) software is performed. All CFD analysis start by creating or exporting windmill geometry from a CAD software like SolidWorks. The geometry used in this case corresponds to an ancient Spanish windmill of XVII century. The software used in domain of CFD for this project is SolidWorks2014. It's an essential tool in almost every branch of fluid dynamics CFD. CFD is commonly accepted as referring to the board topic encompassing the numerical solution of the governing equations which describe fluid flow, continuity and any additional conservation equations. This project shows the study carried out in a final thesis project about ancient windmills in Spain. It intends to design an ancient windmill and explain the aerodynamic performance and application in XVII century. The windmill aerodynamic study is based on the start-up phase. This phase has a great interest because ancient windmills had problems when sails will whirl round frantically until either something breaks or an overheated bearing catches fire. To avoid disaster, the system needs to be fitted with some sort of brake, which can convert the excess rotational energy into heat. On the other hand the research project of Rojas-Sola had already studied the normal operating regime in rotation. The objectives of the research are to establish a 3D CFD model of an ancient Spanish windmill so as to analyse the aerodynamic performance of the ancient Spanish windmill blades: moment, torque, lift, drag, etc. Then it will predict windmill power output at wind speeds: 3 m/s, 5m/s, 7m/s and 10 m/s. Finally it is evaluated its performance depending on tip speed ratio and angular velocity.