In this paper, compounds in the industrial grade and analytical grade furfural were separated and detected under the optimum GC/MS conditions. According to the mass spectrum library searching, mass spectra interpreting and some references, ten compounds were identified:furan, 2,5- dihydrofuran, 2(5H)- furanone, furfural, 5- methyl- 2(5H)- furanone, 1- (2- furanyl)- ethanone, 5- methylfurfural, 5- ethylfurfural, 5- methyl- 2- propionylfurane, and 2- (4- methyl- 2- furyl)- 2- cyclopenten- 1- one. These compounds were quantified precisely by the internal standard method on a PE/XL gas chromatography. The relative standard deviations of the furfural purity were under 3.66% and the recovery of furfural were in the range of 95.2%~101.8%.