The invention relates to a preparation method of a 
halogen-free environmental-friendly synergistic 
flame retardant phenolic foam 
composite material. The preparation method comprises the synthesis process of expandable low-
viscosity phenolic resin by using 
phenol, 
formaldehyde solution, 
paraformaldehyde, 
calcium oxide and alkali catalyst, and the preparation process of the 
halogen-free environmental-friendly synergistic 
flame retardant phenolic foam 
composite material, wherein the synthesis process of expandable low-
viscosity phenolic resin comprises the following steps of: 1) adding the 
phenol, the 
formaldehyde solution and the 
calcium oxide into a reaction container, 2) adding a first batch of 
paraformaldehyde and alkali catalyst into the reaction solution, 3) adding the remaining 
paraformaldehyde and a second batch of alkali catalyst, and 4) adding the remaining alkali catalyst, cooling and discharging the materials to obtain the expandable low-
viscosity phenolic resin; and the preparation process of the 
halogen-free environmental-friendly synergistic 
flame retardant phenolic foam 
composite material comprises the following steps of: taking the expandable low-viscosity phenolic resin, adding surfactant, composite curing agent, halogen-free environmental-friendly flame retardant, carbonizing agent and synergist, evenly agitating, finally adding physical 
foaming agent, evenly agitating the mixture and foaming, curing and molding the mixture to obtain the product. The preparation method has the advantages of simple process, high product stability and wide application scope.