Abstract: Two nonlinear tandem helicopter dynamic models (i.e. the vortex theory model and the momentum theory model) were built separately to trim the helicopter at the hover in the forward and backward flight. A computational method for the stability and controllability derivatives was proposed based on the linear perturbation theory and five-point central difference algorithm. The stability roots of the tandem helicopter in the uncoupled mode were computed using the dynamic equations in the state-space form. Based on the momentum theory model, the stability and controllability of the tandem helicopter were analyzed through using the MATLAB software as the computational platform. The agreement between the computational results and the referenced data indicates that the models are feasible and effective, and they can lay the foundation of the research about the tandem helicopter-s flying qualities.