Finite time disturbance observer ( FTDO) is a nonlinear disturbance observer which has been widely applied to controller designing for nonlinear systems with high-order disturbances． However，in the previous research， FTDO can only be applied to affined nonlinear systems and used to track a desired set-point． In this paper，a FTDO based nonlinear dynamic inversion approach was developed for the tracking control problem of a class of nonaffine pure-feedback nonlinear systems with high-order mismatched disturbances． A fast subsystem was established through the approximate dynamic inversion scheme． In the slow time-scale，the nonaffine system containing outputs of FTOD was transformed into a linear system with affined form to track the time-varying reference trajectory． The effectiveness of the proposed algorithm is independent to the time-scale split character of the original system，and avoids the problem of“explosion of complexity”in backstepping strategy． The simulation results on Matlab / Simulink environment demonstrate that the controller designed in this paper can accurately estimate high-order disturbances in the case of controlled system with nonaffine structure，and the tracking performance is good．