In recent years, the sales of electronic cigarettes (e-cigarettes) have grown exponentially, and the aldehydes in e-cigarette aerosols have raised concerns. This study aims to investigate the effects of key parameters, the ratio of propylene glycol (PG) to glycerin (GLY), the moisture content and the nicotine concentration of e-liquid, and the output power of the smoking device on the releases of aldehydes in aerosols. Laboratory-made e-liquids were filled in a commercial refillable e-cigarette, 50 puffs of aerosols were collected, and the releases of formaldehyde, acetaldehyde and acrolein in aerosols were analyzed by HPLC (high performance liquid chromatography) under the smoking parameters of puffing volume 55 mL, puffing interval 30 s and puffing duration 3 s. The results showed that PG and GLY were the main sources of aldehydes in e-cigarette aerosols, acetaldehyde was mainly from the thermal degradation of PG, formaldehyde was mainly from the thermal degradation of GLY, and acrolein was mainly from the dehydration of GLY at higher temperature. The releases of aldehydes decreased with the increase of the nicotine concentration in e-liquid, while they increased quickly as the output power increased. The effect of moisture content in the e-liquid on the releases of aldehydes was slight.