Considering the tiny elastic elongation of the steel wire rope caused by the force, the vary of the form, the effective tension and elastic elongation with the change of the position of the wire ropes at three different stages of sea surface, water entering and hoisting are analyzed and studied and the numerical examples are solved by Matlab programming. The results show that the steel wire rope is in the form of catenary and near catenary before hoisting the subsea manifold. After the subsea manifold is hoisted, the forms of wire rope are approximately linear, and the effective tension and elongation of the wire ropes increase significantly with the weight increasing of the subsea manifold, and the value maximum of the effective tension occurs at the top of the wire ropes which is a dangerous part and needs to monitor and alert during the installation process. The research results are of guiding significance for improving the installation accuracy and safety in the actual lowering installation process.