Power system security issue is becoming a vital and critical issue for efficient and effective operation of power system network. The power system engineers/operators may face various kinds of issues like outage of generators, transmission lines and loads during operation of the system. The operator should take an instant and correct decision to minimize the effect of such outages for reliable operation of network. This paper aims to solve N-1 contingency problem of transmission line using reactive power performance indexing method. The most vulnerable lines are screened by ranking in order to make ease to give high attention towards such lines during operation of network. For this purpose, two models IEEE-14 Test Bus and Integrated Nepalese Power System network were used.