The MELCOR code is a severe accident analysis code for nuclear power plants. The steam generator dryout time in a station blackout (SBO) accident, which depends on the initial water inventory, is an important parameter in probabilistic risk assessment. Furthermore, the plant transient responses are strongly affected by the initial conditions. To simulate a consistent accident scenario with MELCOR, a correct initial steady-state condition must be generated. However, the current MELCOR users’ manual does not provide a self-initialization procedure. It is quite difficult to achieve the desired initial conditions through a trial-and-error approach. A MELCOR self-initialization algorithm for pressurized water reactor (PWR) plants and its importance in accident analysis is described. First, a MELCOR self-initialization algorithm for a PWR plant is developed and implemented with control functions provided in MELCOR; this is just an input feature in preparing the MELCOR input deck. The initialization work at full-power conditions of the Maanshan nuclear power station is cited as an example. These initial conditions are successfully generated within 50 s with the developed algorithm. Then, the initial responses and the predicted steam generator dryout time in an SBO accident are used to demonstrate the importance of the self-initialization algorithm. This algorithm provides the MELCOR users with a convenient initialization methodology and improves the simulation accuracy.