Kinematic decoupling of parallel mechanisms is a significant characteristic. Parallel mechanism with decoupling features is easy in kinematic analysis, real-time control and industrial applications. The topic was dealt by many scientists and some kinematic decoupled parallel mechanisms were proposed. The design theory for parallel mechanisms was used based on the position and orientation characteristics (POC) and the ordered single-open-chain (SOC), the existed input-output decoupled parallel mechanisms covered 2-DOF to 6-DOF were analyzed for their topology analysis and motion decoupling analysis, from which it can be known that kinematic decoupling can be viewed simultaneously into the topology decoupling and kinematic parameters decoupling. Based on this investigation, four general design rules and principles and the corresponding methods for decoupling parallel mechanisms were proposed respectively, which were based on the synthesis and decomposition of basic kinematic chain (BKC), sub parallel mechanisms, reasonable chosen base point and special prismatic joints configuration. The corresponding examples were designed to illustrate each method. Fifteen novel decoupled parallel mechanisms were totally proposed. Among them, the kinematic decoupling can be divided into position-posture separate decoupling, position-posture internal decoupling, which can be regarded as the direction and roadmap of the kinematic decoupling. The research enriched the numbers of decoupled parallel mechanisms and provided an effective methodology for decoupled parallel mechanisms design.