All inorganic perovskite nanocrystals (AIPNCs) have attracted tremendous research interest due to their fascinating properties in the field of photoelectron. Conventional synthesis of AIPNCs is usually conducted by using batch reactions under gas protection at high temperatures. Herein, an automated microreactor platform consisting of flow-focusing microfluidics is firstly applied to synthesize AIPNCs without gas protection at room temperature. The nucleation and growth is based on the ultrafast mixing and phase separation in low-toxicity solvent. The AIPNCs formed in the microreactor have good crystallinity and narrow size distribution. Meanwhile, the flow-focusing microfluidics also can be used to encapsulate AIPNCs into templated microspheres to improve their stability against temperature, light and water. Furthermore, the as-constructed AIPNC spheres exhibiting linear temperature response represent their promising microthermometer application. It is envisioned that the microfluidic technique provides another alternative to synthesize Ni2+-doped, Ce3+-doped, Yb3+-doped, Bi3+-substituted AIPNCs or organic-inorganic hybrid perovskite nanocrystals and to fabricate templated AIPNC materials and devices.