Abstract: Two kinds of carbon quantum dots, C-dots-160 and C-dots-200 with different fluorescence luminescence behaviors were synthesized by a one-step hydrothermal method at 160 and 200 °C, respectively, using ammonium citrate as the raw material. The relationship between the microstructure of the C-dots and the fluorescence emission behavior was investigated. Results indicate that an increase of synthesis temperature introduces more oxygen and nitrogen atoms into the C-dots, increasing the total number of structural defects and altering their concentation ratio . It is this ratio difference in the two C-dots that causes their different luminescence behaviors. The proportion of several types of defects in the C-dots-200 are relatively balanced, leading to excitation wavelength-dependent fluorescence while the most abundant defects in C-dots-160 are in the form of C＝O, which is the main reason for its excitation independent luminescence behavior. The number of structural defects in C-dots-160 is less than in C-dots-200 and the latter has the stronger fluorescence emission.