Trenching and burying is a common laying method for shallow submarine pipelines, and the method can effectively reduce the risk of submarine pipelines being damaged. In order to further study the jet trenching of submarine hydraulic trencher in stiff clay, a jet trenching system that suitable for breaking stiff cohesive bed was designed, and a series of fixed jet model tests under submerged condition were carried out. The shape, depth, and width of scour hole under different jet conditions were measured, and the effects of clay strength, target distance and jet velocity on the scour hole were studied. The results show that the depth of hole increases logarithmically with increase in jet velocity under constant target distance and clay strength, and the width of hole increases linearly with increase in jet velocity. For low strength (40 kPa) clay, the width of hole increases with increase in target distance, while for high strength (80 kPa) clay, the width of hole decreases with increase in target distance.