Abstarct: Failures of systems make distortions in different levels and it can be considered as a threat to society. So, users expect that systems be reliable and safe. To achieve this goal, research on reliability of systems in all of industries are essential. Drilling equipment is the most important operation unit in mine and mining industries and failure of a part or all of them can be threatened as reduction in production and mining profitability. As yet, many important researches were done on reliability and availability of engineering systems throughout the world, but these researches in drilling operation and equipment aria were baxsed on engineering judgment. To avoid from unpredicted failures and improvements of drilling operation, awareness of machines operating conditions and statistical control of them was considered as a practical approaches. Statistic and probabilistic evaluations are one of the powerful techniques for prediction of failures and making a safe operation of machines. Estimation of probability of failures and safety operation of machines in determined time domain will be possible with using these approaches. In this research, after presentation of probability concepts, definition and reliability modeling in chapter 2 drilling machines have been introduced in chapter 3. Operation subsystems of drilling machines have been introduced in chapter 4. baxsed on this research, Hydraulic, electrical, pneumatic, drilling and transmission subsystems were introduced for the first time. Reliability modeling of any subsystems of drilling machines and drilling fleet in Sarchechme copper mine have been done and presented in chapter 5. Scheduling of preventive maintenance for subsystems of drilling machines has been done baxse on keeping reliability of subsystems at 90% and given in chapter 6 of this research. baxsed on this presented maintenance scheduling, reliability of drilling fleet of Sarcheshme copper mine will be improved by 98%. Finally, details of preventive maintenance schedules have been presented for any of subsystems.