Abstract: In order to explore the occurrence and pollution source of formaldehyde and TVOC in underground stores in Xi'an， a portable formaldehyde gas detector ( Z-300XP) and a portable VOCs gas detector ( Mini 3000) were used to measure indoor formaldehyde and TVOC concentration of 9 underground stores in Xi' an city，and analyze the affecting factors of indoor formaldehyde and TVOC in underground stores． The results showed that pollution of formaldehyde and TVOC in indoor air of underground stores is serious; the mean concentration of formaldehyde and TVOC of each monitoring underground stores were 0. 05 ～ 0. 26 mg /m3 and 0. 34 ～ 3. 56 mg /m3 ; there are 6 underground stores with formaldehyde and 7 underground stores with TVOC concentration exceeding the standard，limit and the exceeding rate reaches 66. 7% and 77. 8%，respectively． The concentration of formaldehyde and TVOC pollutions are more serious in oversize underground stores than those in smaller underground stores; the formaldehyde and TVOC pollution in indoor air of underground stores mainly come from decoration and merchandises sold，and this illustrate that the ventilation volume are not enough in the underground stores．