Abstract: The hydraulic uplift force is critical for assessing Pressurized Water Reactor (PWR) core clamping system reliability. Traditional single-assembly analyses often neglect full-core thermohydraulic coupling, leading to conservative estimates. This study presents a refined model for full-core fuel assembly hydraulic uplift force. Based on subchannel analysis, the model acquires axial thermohydraulic parameter distributions of all core components, integrating hydraulic loads consisting of pressure difference force, momentum force and crossflow force to establish a complete calculation framework. The independent LOTUS software, developed in C++, performs full-core hydraulic uplift force analysis. By comparing the computational results from LOTUS software with experimental and engineering case results, the accuracy of LOTUS was validated. The results demonstrate that the software's calculations closely match experimental data, with a relative deviation of only 1.6%. Under cold operating conditions, the distribution characteristics of hydraulic lift forces in fuel assemblies exhibit a significant correlation with the core flow field distribution. LOTUS accurately calculates hydraulic lift forces for fuel assemblies, providing reliable technical support for their mechanical design and safety assessment.