In recent decades, the technology used to tunnelling in rocks have been developed. Make tunnelling operation safer, more economical, and faster tunnelling are some of this improvements. Studies show that from an economic, environmental and safety standpoint, the use of tunnel boring machines (TBMs) for excavating circle tunnels with lengths of more than 1 km is the best option. Generally, according to the hardness of the ground TBMs are classified to hard rock TBMs and soft ground TBMs. Performance parameters are used to evaluate the performance of hard rock TBMs. The most important of these parameters are penetration rate (PR), advance rate (AR) and utilization (U). Among these three parameters, utilization has a significant impact on the duration of a project and the cost of it. Utilization is defined as the portion of the time that the machine is excavating to the total time. It can be said that all factors causing delay in excavating can reduce the utilization of TBM. The purpose of this research is to evaluate the utilization of hard rock TBMs by considering the rock mass quality. RMR system is used to evaluate the utilization of hard rock TBMs by Regarding the fact that the RMR system, in addition to the ease of calculation compared to other rock engineering classification systems, incorporates many of the rock characteristics. For this purpose, by using the Nowsoud water conveyance tunnel data (Southern Leyleh section), RMR values ??and delays have been calculated. Due to the fact that the most delays in this project were due to bad geological conditions, in this study, the relationship between ground related downtimes (GRRD) and RMR was investigated by using regression analysis in various forms. By regarding the determination coefficients in regression analysis, there is a meaningful relationship between GRRD and RMR. Also, in order to evaluate the utilization of TBM in the Nowsoud tunnel, regression analysis were carried out in various forms. By regarding the determination coefficient values, the best relation to evaluate the productivity of the Nowsoud tunnel (Southern Leyleh section) based on RMR is the quadratic polynomial function. In addition to the above mentioned, in this research, it has been tried to provide a more comprehensive model in order to evaluate the utilization of double shield TBMs according to the rock mass quallty, by creating a database based on the data of several tunnelling projects. The results of regression analysis in various forms show that there is a meaningful relationship between the utilization of double shield TBMs and RMR. Also according to the values of determination coefficients, the best relation to evaluate the utilization of double shield TBMs based on RMR is a quadratic polynomial function. The results of the prediction show that this relationship could predict the utilization with acceptable error.