A set of modified heat transfer formulas were evaluated based on the scaled PRHR HX experiment. Then they were coded into the newly developed Best-Estimation PRHR-MHT Code (PRHR HX-Modified Heat Transfer Code), which was used to evaluate the heat transfer effects of the specific C-type PRHR HX in CAP1400. The applicability of the traditional and modified formulas were evaluated under different engineering operation conditions, and the overall uncertainty was estimated to be within 2%. The sensitive analysis was then carried out to evaluate the influencing factors on the modified formulas in the PRHR HX heat transfer process. The predicted results validate that as much as 60 percent of the temperature difference may drop in the upper horizontal bundle region under some accidental conditions, and the rod bundle effects as well as the cross flow and bubbles disturbances can also enhance the heat transfer effects. The calculation results prove that the PRHR HX design has sufficient safety margin of maximum 27.6% under the ATWS accident, which provide important design references for developing the potential heat transfer capacity, enhancing safe operation, and further optimization of PRHR HX in CAP1400.