Abstract: Many measures have been used to ensure the safety and stability of submarine pipelines and cables. One of the most cost effective methods is to use trenchers and other related equipment to bury the pipeline or cable into the seafloor. In this paper， a light weight， autonomously propelled underwater jet trencher has been designed and conducted underwater trenching tests on the machined prototype model to verify that the designed trencher can trench under submerged condition， and complete the autonomous propulsion work to destroy sand with shear strength of 8kPa when the pipeline flow reaches 50m3/h. The maximum ditch depth can reach 0.41m. This work provides the theory and basis for subsequent model optimization and pipeline burial.

Key words: trencher, submarine jet, autonomous propulsion, ditch and bury