The　structural　character　of　the　I4R　parallel　manipulator　mechanism　was　analyzed,　the　kinematic　parameter　equations　of　the　manipulator　mechanism　were　established　according　to　the　link　length　restrictions　of　the　sub-chains,　and　the　closed-form　positive　and　reverse　position　solutions　were　deduced.　Then,　the　force　Jacobian　matrixes　of　the　manipulator　mechanism　were　obtained　based　on　the　force　balance　relationships　of　the　sub-chains　and　the　movable　platform,　the　configuration　singularity　of　the　manipulator　mechanism　was　investigated　by　means　of　the　line　geometry　method,　and　the　discriminating　conditions　for　the　sub-chain　singularity,　the　platform　singularity　and　the　kinematic　singularity　of　driving　joint　of　the　manipulator　mechanism　were　presented.　Finally,　the　singular　configuration　examples　of　the　sub-chain　singularity,　the　platform　singularity　and　the　kinematic　singularity　of　driving　joint　of　the　manipulator　mechanism　were　presented.　The　results　of　the　study　are　useful　for　design　and　control　of　the　I4R　mechanism.