<p>The underwater vacuum preloading method (UVPM) combined with prefabricated vertical drains (PVDs) has been approved as an effective and environmentally friendly method to improve the engineering properties of underwater marine clay. A large-strain consolidation theory was derived in this paper to investigate the consolidation behavior of marine clay improved by UVPM. The fair agreements between the results from the proposed consolidation theory and laboratory model tests verified its accuracy. Parametric studies were conducted to explore the effects of some key parameters on the consolidation behavior of marine clay improved by UVPM. It is found that the tidal loading accelerates the pore water pressure dissipation at the early-stage of consolidation and induces faster consolidation rate compared to that under static load. The clogging zone slows down the dissipation of excess pore water pressure and thus the consolidation procedure. A rapid application of overlying water head generates higher pore water pressure and accelerates the initial consolidation procedure, while gradual application allows gradually dissipation of the pore water pressure with similar final degree of consolidation eventually reached. Higher seepage resistance delays consolidation procedure but achieves final near-complete dissipation of pore water pressure whereas lower seepage resistance accelerates early rate at the cost of reduced final dissipation.</p>