Meniscus-guided coating exhibiting outstanding depositing accuracy, functional diversity, and operating convenience is widely used in printing process of photovoltaic electronics. However, current studies about hydrodynamic behaviors of bulk heterojunction ink are still superficial, and the key dynamic parameter dominating film formation is still not found. Here, we establish the principle of accurately evaluate the Hamaker constant and reveal the critical effect of precursor film length in determining flow evolution, the polymer aggregation, and final morphology. A shorter precursor film is beneficial to restraining chain relaxation, enhancing molecular orientation and mobility. On the basis of our precursor film-length prediction method proposed in this work, the optimal coating speed can be accurately traced. Last, a 18.39% power conversion efficiency has been achieved in 3-cm2 cell based on bulk heterojunction fabricated by blade coating, which shows few reduce from 19.40% in a 0.04-cm2 cell based on spin coating.