Convective self-assembly technique is of growing importance as a robust technique to arrange various colloidal particles without any templates. Here we focus on stripe pattern formation by the convective self-assembly technique. To unveil the mechanism of the stripe formation process, we employed an in-situ observation of the variation of meniscus shape during the particle assembly process. The observation revealed a following new stripe formation mechanism, which is different from the "depinning" model. A meniscus is elongated downward to be concave toward a substrate as the solvent evaporation progresses. The convective flow toward the meniscus tip accelerates the deformation of the meniscus, resulting in the rupture of liquid film at the thinnest point of the meniscus.