A quantative relationship exists between the structrue and physical properties of organic compounds.The molecular structrue of the examined compounds is selectively described by a molecular distance-edge（MDE）vector.The physical properties of alkanes such as boiling points,density at 25℃,refractive index at 25℃, heat capacity at 300K,Gibbs energy,enthalpy at 300K are estimated with satisfactory results by a novel modified back- propagation neural network method based on the above MDEvectot. A quantative relationship exists between the structrue and physical properties of organic compounds. The molecular structure of the examined compounds is selectively described by a molecular distance-edge (MDE) vector. The physical properties of alkanes such as boiling points, density at 25 ° C., refractive index at 25 ° C, heat capacity at 300K, Gibbs energy, enthalpy at 300K are estimated with satisfactory results by a novel modified back-propagation neural network method based on above MDE part.