Abstract: The mechanisms of addition reaction between alkyl phosphite and butendioic acid dialkylesters as well as that between phosphonobutandioic acid tetraalkyl esters and alkyl acrylate have been disscussed here. The new Synthesis path of 2-phosphonobutane-1,2,4-tricarboxylic acid will give a high yield in practice. The spectroscopy was used to demonstrate the molecular structure of the synthesized product. The physicochemical properties of PBTCA have also been studied.