A novel PEG200 lauric acid diester was synthesized high yield by direct esterification using polyethylene glycol and lauric acid respectively was presented in this work. The product of PEG200 lauric acid diester was characterized by a fourier transform infrared spectrometer(FTIR). The effects of catalyst, reaction time, reaction temperature and molar ratio on the reaction were discussed. The optimum synthetic condition of PEG200 lauric acid diester: esynthesis is based on protection of N2 and the ressure is 0.08Mpa. Using mass fraction 0.45% in p-toluene sulphonic acid as catalyst, molar ratio of polyethylene glycol and oleic acid 1:1.95, reaction temperature about 130-140°C, and reaction time 9-10h. The results of testing of diester products showed that the yield of PEG200 lauric acid diester is 98.2%.And this article reviewed the effect of concentration on viscosity. The characteristic curve of Viscosity-Concentration showed the viscosity increased with increase of the concentration which brought about the increase of particle size. Especially focusing on the maximum viscosity appeard on 80% because of the phenomenon of reverse micelles. Then the viscosity decreased with increase of the concentration.