Disodium octoborate tetrahydrate (DOT), boric acid (BA), magnesium sulfate (MgSO4) and fire retardant DBM were selected as the main ingredients to develop a fire retardant for Southern Pine. A Thermo Gravimetric Analyzer was used to evaluate the temperature effects of Southern Pine samples treated with the DBM. The results showed that Boron-Containing fire-retardant improved Southern Pine fire retardant performance, the mass loss rate decreased, the char yield and the peak temperature of maximum mass loss increased. Thermokinetic method was used to analyze the TG curves of the treated wood, so as to illustrate the DBM treating agent’ mechanism of flame retardant effect on wood, In order to illustrate the activation energy in different combustion stages with quantity, the TG curves were further analyzed by thermokinetic method to obtain thermokinetic parameters of different phases during wood pyrolysis.