The conventional variable structure control(VSC) methods for controlling chaos have some drawbacks, such as high_frequency chattering and the need of a prior knowledge about the upper bound of the uncertainty. Trying to solve the drawbacks, we proposed an adaptive chatteringfree variable structure control(ACFVSC) method for controlling a class of uncertain timevariable chaotic systems towards arbitrarily desired trajectory. The ACFVSC method not only eliminates the chattering phenomenon and tracks arbitrarily desired trajectory asymptotically, but also removes the prior knowledge about the upper bound of uncertainty. Both the asymptotic tracking analysis of ACFVSC and simulation results show that the arbitrarily desired tracking accuracy can be achieved within a finite time if the parameter of ACFVSC controller is appropriately set.