Abstract: Ten intermediate-acidic intrusive rock samples collected from the southwestern margin of the Mohe County basin in northern Da Hinggan Mountains were used to determine the apatite fission track ages. Fission-track ages for these samples range from 72±7Ma to 99±5Ma with mean track lengths varying from 12.5±1.5μm to 13.7±1.8μm. The authors used thermal history simulation software AFTSolve to simulate the thermal history of the samples and the results show two important stages of tectonic movement of northern Da Hinggan Mountains since Late Mesozoic. They are the rapid uplift and denudation stage during the Cretaceous period (120~90Ma) and the rapid uplift and denudation stage since the Paleocene (Ca.60Ma). It is inferred that the formation of these two tectonic movements were influenced by the subduction of the paleo-Pacific Ocean and the subduction of the Pacific Ocean.