The ability to predict and control the coalescence of droplets is of great importance for both industrial and technological applications, including 3D printing, micro-cladding, and self-assembly. Here, a textured surface decorated with nano-pillared arrays was designed and its arrangement density (f) was found to significantly affect the coalescence dynamics of droplets through changing their wettability. A large arrangement density f of the nano-pillared arrays would induce a Cassie wetting state for droplets, which supports the coalescence process. But when decreasing f to a value that produces a Wenzel wetting state, the coalescence is heavily impeded by the nano-pillars. However, a very small arrangement density f is also favorable for coalescence because the pinning effect resulting from the nano-pillars becomes ignored. More importantly, special substrates were well designed by nano-pillars with a density gradient in order to control the coalescence dynamics for some potential applications. This work helps to shed light on the coalescence dynamics of droplets on a microtextured surface modified with different arranged nano-pillars and thereby provides guidance on how to control their behaviors.