Usually, rainfall intensity of a location is interpolated by the rainfalls of weather stations in the neighborhood, not taking topographic effect into account. In this paper, a new method named as rainfall-vector projection is proposed for making the topographic correction. A rainfall vector is composed of a wind speed vector and a terminal velocity of rain drops. The projection of rainfall vector onto the ground surface is the amount for topographic correction. Wind speed vector can be deduced from wind records of standard weather stations. Terminal velocity of rain drops can be obtained by either its relationship to rain drop distribution recorded by disdrometer or on basis of an inference of the specific rainfall pattern of the dedicated rainfall event. Subsequently, a digital terrain model is employed for computing each grid cell of the projected amount of rainfall-vectors. The original rainfall distribution in the area is then adjusted by this correction. A study site in Central Taiwan is selected for demonstrating the topographic correction. The significance of this correction can be concluded by the correction amount of up to 11% of the original rainfalls.