A method of suppressing the multimodal size distribution of InAs/GaAs quantum dots (QDs) using molecular beam epitaxy through flattening the substrate surface is reported in this work. It is found that the surface roughness plays an important role in the growth of QDs through continuous surface evolution (SEQDs). SEQDs are the main components of small QD ensemble in QDs with multimodal size distribution. It is suggested that most of the SEQDs are very likely to nucleate during the growth interruption rather than during the deposition. The growth of QDs on a smoother surface has largely reduced the density of SEQDs. The photoluminescence line width of uniform QDs is found to be only 17 meV at a low temperature. quantum dots, multimodal, surface fluctuation PACS: 68.35.bg, 73.21.La, 68.55.-a