In this paper, melamine (MEL) - formaldehyde resin (VMF) microcapsules were modified by polyvinyl alcohol (PVA) through in situ polymerization. Then the poly ammonium polyphosphate (APP) / mesoporous molecular sieve MCM-41 were coated by the prepared material, and thus a kind of flame retardant (MVMF-(A/M))with novel core-shell structure was prepared. The structure before and after microencapsulating was characterized by infrared spectrum analysis (IR), solubility test and electron microscope scanning (SEM). In addition, the flame retardant was added into natural rubber (NR) and the flame retardancy and mechanical properties of NR composites were tested by oxygen index (LOI), vertical burning test (UL-94), thermal gravimetric analysis (TGA), tensile test. The results showed that the solubility of prepared MVMF- (A/M) is 1.59mg /L in 20 ℃ water, was decreased by 51.2% compared with APP. Meanwhile, MVMF- (A/M) particle surface became rough; compared with other flame retardant system, the limited oxygen index value of the limited oxygen index value of NR- MVMF- (A/M) composites to be maximized, samples could pass the V-0 rating in the UL-94 tests; the tensile strength of samples reached 8.84MPa and its elongation at break reached 310.20%.