Highly oxygenated organic molecules (HOMs) are important precursors for secondary organic aerosols (SOAs). Gaseous sulfuric acid was used as an analogue of HOMs to estimate the ionization efficiency ofHOMs in a chemical ionization atmospheric-pressure-interface time-of-flight mass spectrometer (CI-APi-ToF) equipped with a nitrate chemical ionization source, then a mass-dependent transmission correction for HOMs was performed using a high-resolution half-mini differential mobility analyzer (HR-DMA) in tandem of the ToF-MS, and hence a semi-quantitative method of atmospheric HOMs was established. Based on the method established, a field campaign was then carried out in Beijing from February to March 2018, during which about 110 HOMs species were identified together with their temporal profiles and elemental composition. The observation indicates that hydroxyl radicals play an important role in the formation of HOMs, whereas nitrogen oxides are also involved. Most of the observed HOMs can be classified as extremely low volatility organic compounds (ELVOCs), and followed by low volatility organic compounds (LVOCs), which implies that condensation of HOMs contributes to the formation of secondary organic aerosol in this particular region.