CsPbBrI₂ Quantum Dots (QDs) with good air stability were prepared by hot injection method. The photoluminescence performance of QDs was studied using 375 nm pulsed laser as excitation source. Photodetectors (PD) based on air-stable CsPbBrI₂ QDs were designed and fabricated using a facial spin-coating method. The optoelectronic properties and stability of the devices were also studied in detail.The results show that the quantum dots have strong fluorescence effect near 635 nm, the spectral luminescence peak is relatively narrow, and the half-peak width is about 35 nm. The band gap of CsPbBrI₂ quantum dots is 1.90 eV. As a result, the PDs are capable of broad bandwidth photodetection from deep UV 260 nm to visible 650 nm region with good photoresponsivity of 0.26 A/W, high on/off ratio up to 10⁴ and very short rise/decay time of 3.5 ms/3.5 ms. Furthermore, the device performance shows very little degradation at 25%~35% humidity and 25℃ over the course of 60 days of storages in ambient condition. The combination of high performance broad bandwidth photodetection, remarkable stability and easy fabrication categorizes the CsPbBrI₂ QDs as a kind of very promising semiconducting materials for optoelectronic applications.