Herein, we reported a simple microwave assisted method for synthesizing uniform CsPbBr3 and Cs4PbBr6 perovskite nanocrystals (PeNCs). The phase structure, photoluminescence (PL) emission, and quantum yield (QY) of CsPbBr3 PeNCs can be tuned by changing the radiation time and power of the microwave. The optimized CsPbBr3 PeNCs showed a high PLQY of up to 87%. The transformation from green-luminescent three-dimensional (3D) CsPbBr3 PeNCs to nonluminescent zero-dimensional (OD) Cs(4)PbBr(6)PeNCs was easily realized by adjusting the amount of oleamine (OAm) and oleic acid (OA), and the changes in morphology and phase structure during the transformation process were studied by a microwave-assisted technique. Meanwhile, the optical properties of Cs4PbBr6 PeNCs were revealed by monitoring the changes in absorption and emission spectra. Furthermore, through first-principles calculations based on density functional theory (DFT), the luminescene origination of as-prepared PeNCs was further explained. In this work, we controlled the phase transition from CsPbBr3 to Cs4PbBr6 through a simple method, which provides a strategy for other types of perovskite phase transitions.