Recently, all-inorganic perovskite quantum dots (QDs) (CsPbX3, X = Cl, Br, I) as the emerging semiconductor materials have been intensively studied owing to superior optical properties. Currently, the strategy for preparation of inorganic perovskite QDs mainly focuses on the hot-injection method, but requires inert gas protection and is difficult to mass-produce. In this work, we developed a simple and low-cost strategy for preparing highly luminescent and air-stable all-inorganic perovskite QDs by directly heating perovskite precursors in octane in air. The emission wavelength of CsPbX3 perovskite QDs can be tunable from ultraviolet (UV) to infrared region by simply controlling their halide composition and display high PLQYs. Moreover, CsPbX3 perovskite QDs in octane can exist more than half a year in air and the film of CsPbX3 perovskite QDs also shows good thermal stability and air stability, especially high iodide-substituted CsPbBr3-xIx perovskite QDs. The CsPbX3 perovskite QDs can be easily blended with PDMS and used as color conversion layer on the blue LEDs chip for high-quality white LEDs. Our work opens a window for the potential application of such highly luminescent material in the fields of multicolor LEDs, backlight display and other related optoelectronic devices.