Urea-SCR system is the selective catalytic reduction to reduce nitrogen oxides (NOx) emitted from dieselvehicles. The objective of this study is numerical analysis of 3-dimensional unsteady melting problems of frozen ureaby using an electric heater. It can be applied to determine capacity of power with respect to time and the location of theurea suction pipe in urea storage tank. The study includes the change of liquid volume fraction, temperature profiles anda influence of natural convection by using the commercial software STAR-CCM+(v7.06). The accuracy of thenumerical analysis is estimated by comparisons with experimental data. After validation, a numerical analysis forfreezing urea is conducted with four different heating power. From the results, it was found that relation of velocity ofphase interface and amount of melting urea by increasing heating power in a container. There is also a difference intrend between velocity of phase interface and amounts of melting urea because of effect of natural convection.