In this study, a phosphorus-containing flame retardant, polybis(4-hydroxypheyl)-2-(6-oxo-6-H-dibenzodibenzo [c,e][1,2] oxaphosphino-6-yl) methylene succinate (PHDO) was prepared by melt condensation between (6H-dibenz[c,e][1,2]oxaphosphorin-6-ylmethyl)-p-oxide-butanedioic acid (DDP) and 1,4-benzene dimethanol (PXG). Then, Fourier transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance (1H NMR) were used to characterize the structure of this novel additive. It was added to silicone rubber (SR) in different proportions, and the flame retardant properties together with tensile behaviors of the SR blends were investigated. Results showed that the thermal stability was improved and the burning rate was slowed down after addition of this novel flame retardant. Vertical burning test, cone calorimetric evaluation, and limited oxygen index (LOI) measurement of the samples revealed that the SR with 15 phr of PHDO owned the best flame retardant properties and may pass UL-94 V-0 grade. This improved flame retardant performance may be ascribed to the formation of dense carbon layers, which effectively prevented the surface oxidation and inhibited combustion of the silicone matrix.