The train is an important vehicle in China, but its air quality has important impacts on passengers health. In this work, pollution from carbonyl compounds was measured in the air of six trains. The objectives of this work were to investigate carbonyl compound levels in selected air from trains, identify their emission sources, and assess the intake of carbonyl compounds for passengers. The methods for sampling and analyzing 10 carbonyl compounds such as formaldehyde, acetaldehyde, acrolein, acetone, propionaldehyde, crotonaldehyde, butyraldehyde, benzaldehyde, cyclohexanone, and valeraldehyde in indoor air were proposed with the sampling efficiency, recovery, and detection limit being 92% 100%, 91% 104%, and 0.26 0.82 ng/m3, respectively. It was indicated that the total concentrations of carbonyl compounds were 0.159 0.2828 mg/m3 with the average concentration of 0.2330 mg/m3. The average concentrations of formaldehyde, acetaldehyde and acetone were 0.0922, 0.0499, and 0.0580 mg/m3, accounting for 42.6%, 21.4%, and 24.9% of the total concentrations of carbonyl compounds, respectively. The carbonyl compounds probably came from woodwork and cigarette smoking. The intake of carbonyl compounds for the passengers was approximately 0.043 0.076 mg/h. The carbonyl compounds in train air could be harmful to human health.