A novel strategy was used for preparation of flame retardant based on biomass debris to improve the flame retardant property of silicone rubber (SR). [(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl) methyl]butanedioic acid (DDP) was used to modify diatomite by esterification method, and DDP@diatomite was obtained. The structure and morphology of this novel additive was identified using Fourier transform infrared spectroscopy (FTIR), Brunner-Emmet-Teller (BET) measurements, and X-ray photoelectron spectroscopy (XPS) together with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) techniques. Thermogravimetric (TG) analysis was performed to evaluate the thermal degradation behaviors of diatomite and DDP@diatomite. This novel additive was applied into silicone rubber (SR) composites. Combustion parameters, including heat release rate (HRR), total heat release (THR), smoke production rate (SPR), carbon monoxide (CO), peak smoke production rate (PSPR), peak carbon monoxide (PCO) and vertical burning time, were characterized by cone calorimeter and vertical burning tests. Results indicated that this flame retardant can reduce fire risk and toxicity effectively. TG and X-ray diffraction (XRD) patterns of SR and its composites were also investigated. The inexpensive property of modified diatomite could also expand its fire safe applications. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.