The knowledge of self-assembly is of considerable significance in material science and nanotechnology. Colloidal particles are known to be able to self-assemble into highly ordered structures under both equilibrium and non-equilibrium conditions. Convective self-assembly has been extensively studied experimentally, but a detailed understanding of the underlying mechanisms is still lacking. Modelling and computer simulation methods are increasingly used in the study of colloidal systems. In this research work, we propose a simplified model based on the discrete element method to track particle motions. We investigate the colloidal self-assembly process in aqueous suspensions under the combined influence of fluid flow field and confined meniscus. The equilibrium structure is adjusted by varying the meniscus angle, and the structure formation mechanisms are elucidated in more detail. Various contributions, such as hydrodynamics, electrostatic, van der Waals, Brownian motions, and contact mechanic forces are taken into account in the calculation. As a function of meniscus angle and fluid flow velocity and direction, we find different self-assembled structures and various transition areas at which a growing crystal transits from n to n+1 layer.