A new subject of the solar system dynamics, the orbit dynamics of the Kuiper Belt Objects, is reviewed in this paper. Early Studies were connected with the origin of short-period comets. After the first Kuiper Belt Object (KBO) was found, attentions are turned on the phase space structure of the resonant KBOs. Morbidelli and Malhotra adopted different model to study the sizes of the resonance regions, espically the 3:2 mean motion resonance which Pluto is in. For its orbital characters, Pluto should be called a large KBO. There are other two resonances in its motion, the Kozai resonance and 1:1 super resonance. It is because of these resonances that Pluto keeps its obrital stability. Observations show that lots of KBOs are in mean motion resonances with Neptune. In some early theories, these resonacnes were thought to be caused by catasrophic events such as collision, which can not explain the resonances well for their small probability. Malhotra proposed that Pluto was swept into the 3:2 resonance by planets migration, which happened very easily in the early stage of the solar system. This theory can also explain the resonance formation of KBO successfully.