Melamine polyphosphoric acid rare earth metal salt, synthetic method and application

Melamine polyphosphoric acid rare earth metal salt, a synthetic method and application belong to the field of chemical synthesis. According to the invention, by combining stable melamine polyphosphoric acid with light rare earth elements with unique electron distribution and corresponding electron cloud density, a dual effect of being good in thermal stability, high in phosphorus content and high in char forming catalytic efficiency and improving compatibility and flame-retardant synergistic effect by rare earth coordinate bonding is fully exerted, and the melamine polyphosphoric acid rare earth metal salt can be applied to an intumescent flame-retardant system. The chemical synthetic method comprises a solution method and a calcining method. The formula is shown in the description, wherein M is a rare earth element in lanthanide series, n1 is an integer which is greater than or equal to 2 and n2 is an integer of 1, 2 or 3.