This study proposed an improved atmospheric refractivity interpolation method using mountain weather station data. To overcome the limitations of conventional IDW interpolation techniques that used only upper-air meteorological station data, that inadequately reflected complex terrain effects and local meteorological phenomena in mountainous regions, surface meteorological data from mountain weather stations in Gangwon Province were additionally incorporated. The proposed method developed a novel interpolation technique that propagated surface-level refractivity from mountain stations to the upper layers through an exponential weighting distribution and considered it together with upper-air meteorological data. The performance evaluation through leave-one-out cross-validation demonstrated significant improvements in accuracy compared with conventional methods. The proposed method is expected to significantly contribute to the performance prediction and operational optimization of radar and communication systems operating in mountainous regions.