Lead halide perovskite nanocrystals have been gradually applied in the field of photovoltaic and light-emitting devices. However, the thermal quenching effect hinders the conversion process of materials to light-emitting devices such as LEDs. In this paper, a method for synthesizing CsPbBr₃ nanocrystals using in-situ passivation of organic fluoride at room temperature is proposed, which effectively passivates surface defects and enhances the thermal stability of luminescence. Photoluminescence tests showed that the room temperature fluorescence emission intensity of in situ passivated CsPbBr₃ nanocrystals was approximately doubled compared to pristine samples; When the ambient temperature rises to 100 °C, the passivated sample can still maintain more than 70% of the photoluminescence intensity. After restoring normal temperature, the passivated sample still maintains a stable photoluminescence peak wavelength and intensity for a long time. The test results show that the preparation method proposed in this paper can effectively suppress the thermal quenching of CsPbBr₃ nanocrystals, which is conducive to its application in electroluminescence and down conversion LEDs.