In the present study, two phase pressure drops through the broken cold leg from the reactor pressure vessel side during a loss-of-coolant accident are investigated using computational fluid dynamics (CFD) calculations. Computations have been performed with single-phase water and air, and two-phase mixture, respectively. They are performed with varying the volume fraction of the inlet boundary. As a result, the correlation between pressure loss coefficient and air volume fraction for the system thermal-hydraulic code is determined by the CFD results. The results of this study on the pressure loss coefficients through the broken cold leg can be directly applicable to the evaluation of the reactor safety using the nuclear system code.