With the development of offshore oil and gas platforms and the continuous promotion of offshore wind farms, offshore pile decommissioning will become an important issue. However, the complete removal of offshore piles is complex and significant. The difficulty in removing offshore piles embedded in a cohesive sedimentary bed is usually related to the properties of the cohesive sediments. In this study, we investigated the problem of pile pullout from cohesive sediments under the combined action of a water jet and vibration loading. Through a series of pile pull-out tests, we studied the effects of pile diameter, soil strength, water jet flow rate, vibration intensity, and vertical pull-out speed on the maximum pull-out force of the pile. By combining force and dimensional analyses with test data, we proposed a formula for calculating the maximum pull-out force of a pile embedded in a cohesive sedimentary bed and verified by other researchers.