Abstract: The vibrofloation method without gravel backfill was thought to be proper only for treatment of medium and coarse sand with less than 10% fine particles. Almost no practical project is concerning vibrofloation without backfill treatment of fine sand. In this paper, a laboratory model test was then held to achieve the related characteristics of the hydraulic fine sand. In this test a reduced scale model was set up, in which pressure gauges were embedded. Based on the test data acquired during and after vibroflotation, the formula of porewater pressure dissipation is established. A series of cone penetration tests (CPT) had been made in the test. The insitu tests of single,double and trivibrofloations were conducted under the guidance of model test. According to analysis of results and insitu test model,vibroflotation has been proved to be satisfactory for the improvement of fine sand. 