Abstract: The momentum flux terms are not included in the momentum equations for NOTRUMP-AP600 code. The predicted injection mass flow rate of IRWST and pressurizer level deviate test results largely when NOTRUMP-AP600 code is used to analyze SBLOCA for APEX-600 test facility. The impact of neglecting the momentum flux terms in the NOTRUMP-AP600 was evaluated, including the following contents: The impact of neglecting momentum flux terms for the pressure drop of ADS line was calculated using homogenous model and separated flow model; the detailed two-phase pressure drop was calculated using FLOAD4 code for the ADS4 line, and the result was used to benchmark the ADS4 pressure drop for NOTRUMP-AP600. The results show that the input resistance coefficient should be increased by 60% for AP600 ADS4 line.