In this research, an automatic control system is designed for landing of a small helicopter on a 4 DOF moving platform. The platform has three translational and one directional degree of freedom. The controller design approach is based on development of helicopter nonlinear dynamic model into the SDC (State Dependent Coefficient) form and real time solving of state dependent Riccati equation (SDRE). To compensate the simplifications and term eliminations done to make the SDC form, a nonlinear compensator is added. The performance of the control system in automatic landing is evaluated by computer simulation in different scenarios. The results show a satisfactory tracking performance of the controller during landing on a moving platform.