Abstarct: Today, with the growth and development of the power grid, the continuity of service to consumers and the reduction of grid outages are of paramount importance and are one of the goals of power grid engineers. Maintaining the reliability of the power system at the optimal level is one effective factor among factors that can meet these goals. One way to increase network reliability is to use a high-performance protection system. In order to have a well-functioning protection system, this system must be evaluated routinely by a routine test, because this test reduces relay misoperation or relay false-operation causing by failures that happen in a relay. the failure rate of the relays is one of the effective factors in determining the time interval of routine test. Human error is one of the factors which can play a significant role in changing the failure rate of the protection system. baxsed on the above explanation, in this thesis, the impact of human error on the optimal time interval of routine test and reliability of the protection system is being investigated using a Markov model. To reach this goal, a 5-States Markov model for a transmission line and a 17-States Markov model for power transformer is being proposed. A tip that should be mention here is, the proposed viewpoint for modeling the impact of human error on the protective system is possible for implementation for any protective system. According to the simulation results, the human error affects significantly on increasing the failure rate of protection systems and, consequently, reducing MTTF and optimal time interval of routine test of the protection system.