Among the environments space and oceans have special importance. These environments have serious dangers for human being, for this reason man invented some equipments to access these environments and exploit resources available in them. Some of these equipments are free floating robot and underwater vehicles. These equipments have a mobile base and a manipulator mounted on base. A generic manipulation task is usually given in terms of position/orientation motion trajectories for the end-effector. When the robotic system used to perform the manipulation task possesses more degrees of freedom than those strictly required to execute the given motion of the end-effector it is said to be kinematically redundant. In this sense, an underwater vehicle-manipulator is always kinematically redundant due to the mobility provided by the vehicle itself in addition to the dofs provided by the manipulator. Motion planning of underwater vehicle-manipulator systems (UVMS) is one of the most important aspects for autonomous task execution. The motion planning of a UVMS is a difficult problem because of several reasons. A UVMS is a kinematically redundant system. For a redundant system the inverse kinematics problem admits an infinite number of joint space solutions for a given Cartesian space coordinates, and can be applied aimed at achieving additional control objectives besides the doing main task. In this work an inverse kinematic approach with the ability of preceding between tasks is proposed. In following we design a controller for this system, by considering the studying problem (tracking a path by a robot) and also the nonlinear motion equation for underwater vehicle manipulator, a computed-torques controller is proposed for this system. Trajectories computed from the inverse kinematic are used as desired trajectories in designing controller. In space applications the vehicle uses on-off thruster for position and orientation control, therefore we need to convert the continuous output from continuous controller to discontinuous value. Pulse modulators convert continuous input commands in a sequence of switching signals suitable for the command of on-off thrusters. A pulse modulation scheme based on two modulation curves is proposed for applications in spacecraft position and attitude control using thrusters which may be subjected to switching restrictions. These constraints are taken into account explicitly during the design of the modulation scheme.Finally, considering the fact that a task can be performed by choosing different degrees of freedom of vehicle that some of these cases aren’t suitable in practice, a decision making fuzzy technique is proposed to choose a suitable case from available motions. Keywords: Vehicle-Manipulator, Inverse kinematic, Fuzzy controller, Task priority, On-off thruster, Pulse modulation