A new analytical method of analyzing dimethyl ether (DME) content in liquefied petroleum gas (LPG) is proposed in this paper. An unsolved problem about quick detection of the composition of LPG has been settled with this method. A set of precise preparation apparatus for DME/ LPG solution and a set of quickly analytical system of LPG based on near infrared technology were designed. The analytical equipment can be conveniently connected to the sampling cylinder because it can bear 3.5 MPa pressure. Oblique projection algorithm was used to separate the pure spectra of DME from that of the LPG’s solutions. The standard curve of the concentration of DME (c) has been built by using the Intensity (I) of pure signal of DME in the LPG solution and the concentrations. The correlation coefficient of the equation is 0.999 4. The result of external validation shows that the relative error is less than 2.0%. The new method has the advantages such as fast, easy and noneed of expensive multivariate modeling.