By using computational method of minimum free energy,the effects of dibutyl phthalate(DBP) on combustion carbon residue of double-based propellant were studied. Results show that DBP has a remarkable effect on the production of carbon residue in the combustion of double-based propellant. A critical value of DBP content exists in the combustion of the propellant. When the threshold has been exceeded,the combustion of double-based propellant can generate carbon residue,and the concentration of carbon residue will increase with the DBP content. To lower the combustion pressure or increase the nitroglycerine content of the propellant can increase the critical value. In addition,the function of the critical value of DBP content and the nitroglycerine content,combustion pressure is established based on the computational results.