The residues of dimethoate pesticides in the environment and agricultural products pose a great threat to human health and the ecological environment. Therefore, it is urgent to establish an efficient, simple and inexpensive method for detecting dimethoate. This study used a simple method to prepare N-doped carbon quantum dots (N-CQDs) via hydrothermal treatment of xylose and ammonium bicarbonate. The excitation spectrum of N-CQDs exhibited dual fluorescence centers at 238 and 330 nm, while both of their emission centers were located at around 402 nm. The fluorescence center obtained at the excitation wavelength of 238 was quickly quenched by dimethoate within 1 min, while that obtained at 330 nm showed little change. On this basis, a dual fluorescence center-based ratiometric fluorescent probe for dimethoate detection was constructed. Under the optimal reaction conditions, the linear ranges for dimethoate detection were 2~100 and 100~180 ng·mL-1, with a limit of detection of 0.67 ng·mL-1. Common ions and pesticides showed little effect for dimethoate detection, suggesting a good selectivity of the constructed probe without needing specific enzyme labeling. Moreover, the as-constructed probe was applied to detect the dimethoate residual in the actual pitaya samples, and the results were compared with the standard GC-MS method. The recoveries of the established probe were between 92.55% and 102.24%, with RSD lower than 3.62%. The recovery of the GC-MS method was between 84.22% and 100.64%, with RSD lower than 10.95%. Results reveal that the established probe shows higher accuracy and precision than the standard GC-MS method, the result is satisfactory.