Flocculation-solidification combined (FSCM) is a reasonable choice for the treatment and recycling of dredged mud slurry at extra high water content (EHW-MS). However, FSCM tends to show some limitations when the treated EHW-MS is recycled as filling material with high requirement on mechanical properties. In order to improve the treatment efficiency of EHW-MS, a new method is proposed, i.e., vacuum preloading-flocculation-solidification combined method (VP-FSCM). A series of laboratory model tests are done to verify the advantages of the VP-FSCM, and to identify the variation of its treatment advantages with the equivalent initial water content. In addition, the internal mechanism and feasibility of VP-FSCM are analyzed and demonstrated by micro-tests (e.g. XRD and SEM). The results show that the undrained shear strength of the VP-FSCM treated EHW-MS can be increased to 1.65 times than that of FSCM, and the strength advantage is maintained at least 1.2 times. On the micro level, the advantage of VP-FSCM is that the quantity and development of hydration products such as C(A)SH gel and ettringite have been significantly improved, and the soil structure has been further filled and compacted.