[Objective] To analyze the main chemical constituents of decoction and concentrated decoction of Rhizoma Acori Tatarinowii (RAT) by gas chromatography-mass spectrometry (GC-MS). [Methods] RAT was decocted and concentrated in the pottery for two times and then 6 batches of the decoction and its concentrated decoction were analyzed by GC-MS. [Results] Five kinds of components in a higher amount were found in the first and second decoction of RAT, including: ?-asarone, ?-asarone, 2, 3-dihydro-3, 5-dihydroxy-6-methyl-4H-pyran-4-one, 5-hydroxymethylfurfural and acoramone. The contents of volatile components of ?-asarone and ?-asarone were lower while those of water-soluble components higher in the concentrated decoction of RAT. [Conclusion] The therapeutic effect of RAT is the co-action of the multiple components of RAT; the effect is related not only with the volatile components but also with the water-soluble components. Therefore, more attention should be paid to the difference of components in the concentrated decoction, which is generally used in the research of new Chinese herbal medicine, and in the clinically used decoction.