Formaldehyde (HCHO) is one of the most important trace gases in the atmosphere.Its closely related to human health and the environment and plays an extremely important role in tropospheric photochemical reactions. In recent years, the autumn tropospheric ozone and HCHO pollution problems in the Pearl River Delta (PRD) region of China have become more serious, and the tropospheric HCHO is one of the key indicators for analyzing the formation mechanism of the boundary ozone. Therefore, it is of great importance for us to carry out the HCHO observation experiments in the PRD region. This study retrieved the differential slant column density (DSCD) of O4 and HCHO at HeShan Observatory from September 20 to October 3, 2019 using the multi-axis differential optical absorption spectroscopy (MAX-DOAS) technique. The air mass factor (AMF) of HCHO was calculated using the geometric approximation method, thus obtaining the tropospheric HCHO vertical column density (VCD). The results showed that the tropospheric formaldehyde VCD fluctuated between 4.99×1013 and 6.48×1016 molec·cm-2 during the observation period, with an average value of 2.18×1016 molec·cm-2. The retrieved tropospheric HCHO VCD was almost consistent with that from TROPOspheric Monitoring Instrument (TROPOMI), with a correlation coefficient (R) of 0.80. However, the tropospheric HCHO VCD from TROPOMI on 25 and 28 September was lower (about 25%) than that from MAX-DOAS, which may be caused by the different observation methods. In addition, the retrieved O4 and HCHO DSCD and HEIdelberg PROfile (HEIPRO) algorithms based on the optimal estimation method were used to retrieve the tropospheric aerosol and HCHO profiles during the observation period. The results showed that the HCHO pollution was mainly concentrated near the surface (0～800 m), and the HCHO pollution during the observation period mainly came from the local industrial and motor vehicle emissions. The retrieved surface HCHO from MAX-DOAS was compared with that from 2,4-dinitrophenylhydrazine chromatography technique. The surface HCHO from MAX-DOAS showed similar trends with that from the 2,4-dinitrophenylhydrazine chromatography technique. The high values (up to 14.31 μg·m-3) of surface HCHO from 27 to 29 in September were simultaneously monitored, with the correlation coefficient (R) and slope of 0.88 and 0.98, respectively, which validates the reliability of surface HCHO results retrieved from MAX-DOAS technique.The results of this study show that the MAX-DOAS technique can realize the real-time monitoring of tropospheric HCHO VCD, which can be used as an important means to verify satellite-based measurements. The tropospheric HCHO profiles can be retrieved using the MAX-DOAS technique.