Abstract: Experts expect that underwater tee joint has an wide application perspective in the areas where submarine pipelines are laid intensively. It is the first time in China that the underwater tee joint of bi-directional pig is applied in the first phase of the exploitation project of Suizhong 36-1 Offshore Oilfield. Compared with the general Y-shaped joint and turnable Y-shaped joint, the bi-directional pigging for main pipe and branch pipe can both be realized by using the underwater tee joint, the cleaning operation will not be restricted along the direction of oil and gas transmission, and this can make the general layout of submarine pipelines greater flexibility. The pre-installation method of underwater tee joint using equal-length pipe is presented to offset the existed defects in ordinary installation methods of underwater tee joint. The equal-length straight pipes are laid in advance with pipe-laying vessel to replace them with equal-length underwater tee joints. This method can improve the efficiency of pipeline construction, reduce the installation difficulty and risk, and save engineering investment, which can be used for reference in offshore petroleum projects.