A simple, economical and green synthesis method for the preparation of water‐soluble carbon quantum dots (CQDs) has been developed via hydrothermal treatment of fresh cherry tomatoes without any other reagents. The as‐prepared CQDs exhibited excellent excitation‐wavelength‐dependent photoluminescence property and high selective response to trifluralin over other selected herbicide in soil samples, thus, a CQDs‐based sensing platform for trifluralin determination was established by evaluating the change of the fluorescence intensity of CQDs with trifluralin. Under the optimized conditions, the sensing system displayed a linear relationship with the trifluralin concentrations in the range of 0.050‐200 μM, and the limit of detection (LOD) was 0.5 nM. Satisfactory repeatability, reproducibility, recovery results (94.6‐103.2%) are achieved for the determination of trifluralin in real soil samples. Real sample study in soil samples revealed that the proposed sensing system was promising for applications in environmental monitoring.