A flame retardant wood was prepared using a series of insoluble stannates through the double bath technique. The flame retardancy of the wood samples was studied with the LOI method. The relationships between the flame-retardant performance and the thermal property of wood were studied by the thermogravimetric analysis (TGA), differential thermogravimetry (DTG), differential thermal analysis (DTA) and scanning electron microscopy (SEM) methods. The results show that the insoluble stannates, which were precipitated into the wood by the double bath technique, can obviously improve the flame retardancy of wood. Na2SnO3 can catalyze the intermolecular dehydration reaction and increase the stability and amount of the char residue, and the metal ions not only catalyze the intermolecular dehydration reaction in the second stage but also changed the degradation reaction of the char residues in the third and fourth stages.