An analytical investigation of the loop seal clearing (LSC) in the small-break loss-of-coolant accident (SBLOCA) for direct vessel injection (DVI) line and cold leg (CL) breaks was performed using the MARS-KS code. LSC behaviors of the ATLAS test and analyses showed quite similar trends with each other, but those of the APR1400 analyses, different from the ATLAS test and analysis. With respect to the effect of modeling, the LSC behaviors showed a strong dependence of the system and component modelings. Critical thermal hydraulic parameters important to reactor safety, i.e., core and downcomer water level, cladding temperature, and crossover leg (COL) water level, were also evaluated for the two typical scenarios of an SBLOCA. Most of the thermal hydraulic behaviors were greatly dependent on the system and component modelings of the MARS analyses including the multi-dimensional effect of the reactor vessel (RV) and the application of the counter-current flow limit (CCFL) model.