Reliability is a very important factor in the operation of a distribution network system. Some parameters that can be used as a reference in knowing the reliability of a distribution system that is by calculating SAIFI (System Average Interstuption Frequency Index) calculation index the average number of disturbances for three years. SAIDI (System Average Interruption Duration Index). The average duration index of interruption for three years. CAIDI (Customer Average Duration Intteruption Index) In this research that is calculate reliability index value using calculation of value of SAIFI, SAIDI and CAIDI in Substation Medari then compare with SPLN performance target. 68-2: 1986 and IEEE std 1366-2003. Based on the results of calculations and analysis can be said the most reliable is the calculation of SAIFI in 2014, 2015 and 2016 because the value does not exceed the standard SPLN no. 68-2: 1986 is 3.2 times / customer / year, but in 2014 only one repeater exceeds the SPLN standard no. 68-2: 1986 is on the MDI 01 feeder because the value of SAIFI is 4.59 times / customer / year