The absorption of atmospheric water vapor gradually weakens from the microwave to the visible band, but the absorption in the ultraviolet band has been ignored. Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a passive optical remote sensing technology that can simultaneously retrieve a variety of trace gases such as NO₂, SO₂, HCHO, HONO and water vapor. It is often used for regional atmospheric three-dimensional distribution and transportation monitoring, and has the characteristics of low cost, high time resolution stability, and real-time monitoring. Water vapor is an important greenhouse gas, and the water vapor absorption in the ultraviolet band is often not considered when we retrieve trace gases, which may affect the retrieval of trace gases in the ultraviolet band, resulting in systematic errors. This study introduced the atmospheric water vapor retrieval in the ultraviolet band using MAX-DOAS observations in Qianxian, Xi'an, from June 1 to September 24, 2020. The optimal retrieval band in ultraviolet and visible were selected andcompared. The comparison results confirmed the water vapor absorption in the ultraviolet band, and we also evaluated the influence of ultraviolet water vapor absorption on the retrieval of trace gases in the same band. First, the optimal retrieval bands for water vapor in the ultraviolet (351~370 nm) and visible blue bands (434~455 nm) were selected according to the root mean square (RMS) and the absorption cross-sections of H₂O and O₄. Secondly, the O₄ and H₂O DSCD in the ultraviolet and visible blue bands were obtained by DOAS fitting, and the correlation between the two bands was analyzed. The two bands' correlation coefficient of O₄ and H₂O DSCD in the two bands were 0.85 and 0.80. The ratio of O₄ and H₂O DSCD in the same band has also been analyzed, and the correlation coefficient in the two bands was 0.89. The high correlation coefficients of H₂O DSCD and the ratio of H₂O DSCD/O₄DSCD in the ultraviolet and visible blue bands indicate that even Xi'an, which has a lower water vapor concentration relative to coastal cities, also has water vapor absorption in the ultraviolet band near 363 nm. It will affect the retrieval of other trace gases in the ultraviolet band using DOAS technology. Finally, the retrieval errors of gases (O₄, HONO, and HCHO) that may be affected by water vapor absorption in the ultraviolet band were evaluated. The water vapor absorption in the ultraviolet band will increase O₄DSCD, HONO DSCD, and HCHO DSCD during the fitting process, corresponding to the changes of +1.16%, +8.55%, and +9.04%, respectively.