Kilauea Iki Lava Lake, a lava lake in Hawaii Island, was formed during the summit eruption of Kilauea Iki caldera from late 1959 to early 1960. It has been a closed system since the event since no material was added after its formation, and it then became an excellent place to study magma differentiation. During cooling, different minerals cool at different temperature due to their difference in composition, and magma gradually differentiate along with temperature decrease. Thus, by knowing the primary composition of the magma, the differentiation pattern can be indicated. In order to observe differentiation process, the changes in oxide content in the remaining liquid were compared with MgO, the temperature-related oxide. In this project, MELTS, a software package designed by Mark.S.Ghiorso is used for my analysis. By utilizing MELTS, weight percentage of oxides vs MgO models can be calculated with known primary composition and assumed temperature, pressure and volatile content. After adjusting the model by comparing with real sample data of cooled lava, reliable models of content of oxides can be generated to be a strong indicator of differentiation process, and can be used in future studies of Kilauea Iki Lava Lake.