Abstract: Xenon oscillation is a problem that cannot be ignored in large thermal neutron reactors. Serious xenon oscillation brings sever challenges for axial power controlling.Through analyzing xenon oscillation of Unit 2 of Qinshan II, the oscillation divergent and convergent law is found. In the process of xenon oscillation, if moving the control rod, which leads to the axial power deviation ΔI changing opposite to the current trend, can effectively prevent xenon oscillation. On the contrary, it may exacerbate xenon oscillation. Then the law is verified by xenon oscillation attenuation and intensification processes of Unit 3 of Qinshan II.Finally, some reasonable suggestions for preventing xenon oscillations are put forward, which provides important guarantee for the safe and stable operation of the unit.