The carbon dots（CDs）were synthesized by one step hydrothermal method using the plant soot as raw material.Effects of plant soot amount，concentration of H2O2 solution，pH value of reaction solution，reaction time and temperature were also discussed.The maximum excitation and emission wavelengths of CDs were 340 nm and 450 nm，respectively，and no red shift was observed with the increase of excitation wavelength.The Fourier-transform infrared（FTIR） spectra characterization demonstrated that CDs contained lots of —COOH and —OH groups on their surface.The synthesized CDs could be used as a tool for the detection on chlortoluron as their fluorescent intensity could be selectively quenched by chlortoluron.The linear range of the method for chlortoluron was 0.15-3.15 mg·L-1，with a correlation coefficient（r2） of 0.999 3 and a detected limit of 0.05 mg·L-1.The proposed method was applied in the detection of chlortoluron in irrigation water samples with recoveries of 93.3%-112% and RSDs not more than 4.9%.Meanwhile，the influences of pesticides with similar structures to chlortoluron and common ions on the system were investigated，and the quenching mechanism for chlortoluron toward CDs was also discussed.