The dynamic growth process of gold nanoflowers (AuNFs), which have ample distinct optical properties important for chemical and biosensing as well as high catalytic efficiency, is essential for the controlled synthesis of AuNFs. Here, a simple and rapid microfluidic strategy is developed not only to synthesize AuNFs of various sizes but also to investigate the growth process of AuNFs, which surprisingly allows for the observation of previously unidentifiable processes. These AuNFs are quasi-spherical with many branches in various orientations and poly-crystalline with different crystal faces. The detailed process about the aggregation of primary nanoparticles in the growth process of AuNFs is deconvoluted into a dynamic self-limiting growth process, which is controlled by electrostatic repulsion and van der Waals attraction between building blocks. Monte Carlo simulation confirms the self-limiting growth process. Meanwhile, the as-prepared AuNFs show a high catalytic activity for the reduction of 4-nitrophenol (4-NP) by NaBH4 while not necessitating post-washing treatments.