The invention belongs to the field of polymer foam, and discloses intrinsic flame-retardant modified melamine formaldehyde foam as well as a preparation method and applications thereof. The preparation method utilizes flexible segments of PVA (polyvinyl alcohol) and characteristics of containing active amino and having cohesiveness of a silane coupling agent KH550; by using a special process, PVA and KH550 can participate in the reaction of melamine formaldehyde, so that PVA and KH550 chains are embedded between rigid groups of melamine formaldehyde, so as to improve the characteristics that the foam is easy to be brittle and pulverized and has poor toughness in the case of meeting flame retardant requirements. According to the invention, the prepared melamine formaldehyde foam has good flexibility, has a certain compressive strength, and has the oxygen index larger than 34% and the elastic recovery rate up to 90%.