Abstract: The effects and causes of abnormal tracks of tropical cyclones are studied using the mathematical model of motion curvature. It is found that the changes in curvature of thetropical cyclone tracks are related with Coriolis parameter, ambient pressure distribution, moving speed, vortex dynamics and frictional force for the underlying surface. When these factors gradually change to meet the criterion of the so - called " crescent point " and superimpose evolving curves, the solution moves out of the superimposing domain as result of changes inexternal sources, the tropical cyclone will change direction abruptly, leaving abnrmal tracks.