We systematically investigated the morphological evolution of thin polymer blend films via annealing in mixed solvents. Here, a simple and efficient approach was proposed to fabricate different complex polymer nanostructures based on the dewetting of polymer blend films in mixed solvent. First, the nanobowl structures of poly (methyl methacrylate) and pi-conjugated polymer-poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] were fabricated using this method. In addition, we also found that reversible dynamic transition among complex polymer structures could be achieved. This allowed us to reversibly adjust the complex structures by different external stimuli. Finally, it was determined that various arrays of complex polymer nanostructures, such as Janus nanostructures, core-shell nanostructures, nanobowls, nanochannels, and nanotubes, could be fabricated by pre-patterning the thin polymer blend films.