Aiming at risk reduction and cost reduction for cable casing post-installation considering the risk anchoring, 3 kinds of methods were comparatively analyzed, such as anchor mooring crane, DP vessel and on-platform installation and the results show that the on-platform installation method had great advantages in installation period, cost and safety. Based on the theoretical analysis, this paper designed a new method of cable casing installing without anchor mooring crane, which is verified by the actual case. The new process can not only reduce operational risk, but also reduce project cost,which can be saved by 3 days vessel date.The method can provide important reference significance for the installation of cable casing on the platform in service, and is expected to be promoted in the future.