Though sulfuric acid and ammonia/alkyl amines are recognized as main contributors to new particle formation (NPF), models and observations have indicated that other organic species may be involved. In this study we introduced a suitable flow tube system to investigate the effect of formaldehyde (CH2O) on NPF from sulfuric acid and water at 297 K. Our results showed that nucleation rates are slightly enhanced when adding CH2O of 0.31-2.40 ppbv (in the range of atmospheric CH2O peak concentration) to stable sulfuric acid and water system at relative humidity (RH) of 30%, i.e., a rise of the particle number only by a factor of about 2, which is small in comparison to the millionfold increase caused by methylamine in similar conditions. And the promoting effect was weak under different RH. Cluster growth flux at experimental conditions, obtained from quantum chemistry-based cluster evaporation rate constants applied in a cluster population dynamics model, showed H2SO4-CH2 Obased clusters are hard to grow. Therefore, the effect of CH2O on NPF via directly involving in the nucleation can be eliminated. In addition, the derived information may provide new insight into the impact of aldehydes on NPF.