Today, with the increasing advancement of technology, the need for energy is also increasing and due to the high cost of energy production, reducing its waste is very necessary. Earth excavation is one of the important activities in the geotechnical, mining and oil industries. The use of TBM in digging underground spaces is increasing day by day due to its many advantages over traditional and other mechanized methods. The most important criterion for measuring the amount of energy consumption in TBM is the specific drilling energy, which is equal to the amount of work done to dig a unit volume of rock. Theoretically, this energy should be equal to the area under the complete stress-strain curve, which is called the strain energy of the rock mass, but in reality, a large amount of energy is wasted for various reasons such as excessive crushing of the rock, overcoming the friction between the rock and the cutting tool, or energy waste in mechanical parts. The aim of this research is to estimate the energy waste ratio in rocks of different quality using real data recorded in TBM drilling. Based on rock behavior models, the energy loss ratio in TBM excavation was determined. The second section of the Karaj-Tehran water transfer tunnel project was used as a case study. Accordingly, by calculating the ratio of specific drilling energy to strain energy and the strain energy ratio for rock mass and determining the relationship between these two parameters, the energy loss ratio was determined in rocks of different quality. The research results showed that the specific drilling energy is directly related to the increase in depth and quality of rock mass. The strain energy ratio (Ψ) and energy loss (ʎ) have an inverse relationship with each other, and relationships were presented to predict the amount of energy loss based on the strain energy ratio in rocks of different quality.