Organic-inorganic hybrid perovskite with large crystal size and high quality are desirable for making high-performance solar cell. However, the expectant film with good surface is normally limited by various factors, such as under-layer, film thickness. Here, an efficient dual effect method on the performance by means of under layer abduction strategy is developed to improve perovskite crystallization by incorporating nitrogen-doped reduced graphene oxide into nickel oxide as hole transport layer, which significantly improves the electrical conductivity, and endows composite material with encouraging hydrophobic property. In addition, the modified under-layer enhances the space of crystal nucleation and facilitates crystal growth through grain boundary migration, thereby achieving large crystal size and reduced grain boundaries. Consequently, a best device with maximum power conversion efficiency of 18.84% is achieved due to a significant improvement in fill factor and short-circuit current density. Moreover, its flexible application shows an efficiency of 14.11%, retaining > 90% after aging for 1200 h without encapsulation. This work provides a potential platform to fabricate low cost and efficient hole extraction materials for large scale and flexible perovskite solar cell.