Fluorescent carbon quantum dots (CQDs) are new and promising photoluminescent nanomaterials. They have many advantages, such as diverse physicochemical properties, unique optical properties, low cost, eco-friendliness and abundant functional groups, which make them have broad application prospects in biological imaging, optoelectronic devices, photocatalysis, ion detection, targeted drug delivery and other fields. Light-emitting diode (LED) has been the focus of academic research for many years, widely used in liquid crystal displays, full-color displays and daily lighting equipment. Many kinds of fluorescent materials have been applied in LED research. Nano fluorescent CQDs have great application prospects in optoelectronic devices because of their advantages ofadjustable fluorescence emission wavelength, stable luminescence performance, environment friendliness, abundant raw materialsand low cost. However, the controllable preparation of CQDs is still a challenge. The fluorescence emission wavelengths of most CQDs are mainly concentrated in the blue and green wavelengths, and the quantum yield is low, which limits the development of CQDs in this field. Therefore, the synthesis of fluorescent CQDs covering thefull visible spectrum and the briefly analysis of their luminescence mechanism can greatly promote the application of CQDs in the field of white LED. In this paper, full-color fluorescent CQDs were successfully prepared by a one-step solvothermal method using triammonium citrate as the precursor and various low-toxic and inexpensive acid reagents as modifiers. The prepared CQDs were characterized by fluorescence spectrometer, transmission electron microscope, X-ray diffractometer, Raman spectrometer, X-ray photoelectron spectrometer, ultraviolet-visible spectrophotometer and Fourier transform infrared spectrometer. The results showed that the prepared CQDs had uniform size and good dispersion, the emitted fluorescence gradually changed from blue to red, the emissionpeak wavelength was adjustable between 450 nm and 650 nm, the fluorescence quantum yieldswere all above 30%, and the quantum yield of red CQDs was as high as 38.75%. The surface of the prepared CQDs was rich in carboxyl and hydroxyl groups, which gave them strong hydrophilicity. The luminescence mechanism of CQDs were explored by controlling the degree of graphitization and the number of carboxyl groups on the surface by different acid reagents. Full-color emission CQDs/epoxy composite films were prepared by adding one or more colors of CQDs to the epoxy resin, and three kinds of white LEDs with high color rendering index were successfully prepared. The CIE color coordinates of the warm white LED were (0.43, 0.39), the correlated color temperature was 3 913 K, and the color rendering index was 86. The CIE color coordinates of the prepared neutral white LED were (0.37, 0.37), the correlated color temperature was 4 170 K, and the color rendering index was 85.5. The CIE color coordinates of the prepared cold white LED were (0.30, 0.34), the correlated color temperature was 6 857 K, and the color rendering index was 80.4. This study provides a new idea for developing alternative phosphors for low-cost full-color fluorescent films and light-emitting devices.