Reverse engineering is an important method utilized in manufacturing and design process. When there is no technical data of a product or it is unusable, the CAD model is obtained with this method. After obtaining the data of the existing product, rehabilitation studies are carried out for improvement in the design. In this rehabilitation process, numerical methods can be used to optimize the current product. This study presents a reverse engineering process of detecting the reasons for lack of performance of an actual hydraulic turbine runner. Reverse engineering methodology is applied for Kahta H.E.P.P. in Turkey, Adiyaman which has two identical horizontal Francis type turbines. The head and discharge are 125 m and 3.25 m3/s per turbine, the power plant capacity is 3.66 MW and overall turbine efficiency is 92%. According to the results of this study, it is determined that the turbine runner blade trailing edge theta angle causes a large recirculation region which drops the performance of the turbine.