Reliability is the level of performance success of a system or part of the system, to be able to provide better results over a certain period of time and under certain operating conditions. To be able to determine the level of reliability of a system, can be done by performing calculations and analysis of the success rate or operation of the system under review, at a certain period and then compare it with predefined standards. There are several parameters that can be used to determine the reliability level of the power distribution system by calculating the average number of system interruptions during the year or SAIFI, the average duration of system disturbance index for one year or SAIDI (System Average Drop Duration Index) and CAIDI (Customer Disruption Duration Length Index). The method used to calculate the reliability level of the electric power distribution system is by using MATLAB, which will later function as a calculator using the GUI (Graphical User Interface) found in MATLAB. Based on the calculation and analysis that has been done, it can be seen that the reliability value of the Bantul Substation 150 kV during 2018 can be said to be reliable for the SAIFI value according to the SPLN standard No. 68-2: 1986 and WCS (World Class Service) and WCC (World Class Company), while according to IEEE standards 1366-2003 can be said to be less reliable for its SAIFI value. Furthermore, the value of SAIDI in the 150 kV Substation of Bantul can be said to be less reliable in 2018 in accordance with the IEEE standards 1366-2003 and WCS (World Class Service) and WCC (World Class Company), but according to SPLN standards No. 68-2: 1986 can be said to be reliable for its SAIDI value. In addition, the value of CAIDI in the 150 kV Substation of Bantul in 2018 can be said to be less reliable based on the IEEE std 1366-2003 standard.