A new method of introducing castor oil based flame-retardant polyols (COFPL) into polyurethane foams was explored in this paper. Castor oil was alcoholyzed with glycerol. And epoxidation of glycerolysis castor oil was carried out by formic acid and hydrogen peroxide (H2O2). The flame-retardant polyols were gotten though ring-opening reaction with diethyl phosphate. A novel castor oil-based polyurethane foam has been prepared by a one-shot process with and without COFPL.