In order to meet the needs of changing positions and orientations in large-scale product testing and large workpiece operating, such as machining, welding and spraying, this paper presents a planar decoupled parallel manipulator driven by three sliders. This simple but practical mechanism is capable of realizing a large workspace. The direct and inverse kinematical solutions are derived. The working spaces of the end operator are carried out when it is in given positions and given orientations. The simulation demonstrates that all kinds of straight lines and circles can be realized by the end operator of the mechanism, which the corresponding motion disciplines and characteristics of the three sliders are also obtained. Last, the virtual prototype of the manipulator is given. The paper lays the foundation for the manufacture, the real-time control and industrial application of the 3-DOF parallel manipulator.