A halogen-free phosphorus-containing flame-retardant rigid polyurethane foam plastic and a preparation method therefor. The halogen-free phosphorus-containing flame-retardant rigid polyurethane foam plastic comprises a phosphorus-containing reactive flame retardant 9,10-dihydro-9-oxa-10-phospha-10-oxidized phenanthryl terephthalyl alcohol, the chemical structural formula thereof being (I). A series of flame-retardant rigid polyurethane foam plastics with different phosphorus contents can be prepared by changing the dosages of a flame retardant and a polyether polyol. The phosphorus-containing foam plastics can generate a phosphorus-rich coke layer with a better heat stability when decomposed, and the phosphorus-rich coke layer can inhibit the continuous combustion of the matrix resin and can also effectively inhibit the generation of a combustible gas.
