This paper, presents the effect of a cable line on the maximum overvoltage location along cable line and reliability indices in the power system with the combined transmission line (overhead line/cable line). Maximum overvoltage has a vital role in insulators design of high voltage cable. On the other hand, recently with the extension of power systems, maintaining the high degree service reliability is very important. High voltage cable insulations have undesirable effect on power system reliability. Therefore, in this study, the effect of cable line length and the number of span before a cable line are investigated on the amount and location of maximum overvoltage. Furthermore, reliability indices are determined by changing length and age of a cable line in combined transmission line. Results show that cable line length does not change the maximum overvoltage location but has significantly effect on the amount of maximum overvoltage. Also, length and age of cable line effect on power system reliability indices considerabl