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In the era of requirements in indoor air quality, liquid desiccant (LD) dehumidification is regarded as an energy-saving method removing indoor air contaminants during the dehumidification process, which has made considerable progress in recent years. Many previous studies have confirmed that the heat and mass transfer characteristics associated with absorption characteristics and thermophysical properties in LDs play a vital role in contaminants removal performance. The main purpose of this research is to numerically assess the indoor formaldehyde removal performance of a LD dehumidification system with different LDs. In order to make a fair assessment, a novel criterion based on the same temperature and the same vapor pressure which is the same desiccant condition is proposed. A numerical model integrated with heat, moisture, and formaldehyde transfer is used to predict the system performance. This model can rationally simulate the formaldehyde removal performance of the LD dehumidification system by inputting various operating parameters, including indoor air status parameters and outdoor air status parameters. The simulation results show that the number of mass transfer units of formaldehyde (NTUmf) plays a key role in the formaldehyde removal performance. The formaldehyde removal performances decrease with the increase of temperature and humidity ratio of return air, while they increase with the increase of temperature and humidity ratio of fresh air. With the aforementioned results, the study is expected to be beneficial to further improve the removal ability and potential of LD systems for indoor formaldehyde.