In this work, p-phenylenediamine and L-cysteine were used as raw materials, and water-soluble N, S co-doped carbon dots (N, S-CDs) with excellent performance were prepared through a one-step solvothermal method. The morphology and structure of N, S-CDs were characterized by transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, and the basic photophysical properties were investigated via UV-Vis absorption spectra and fluorescence spectra. Meanwhile, the N, S-CDs have excellent luminescence stability with pH, ionic strength, radiation time, and storage time. Experimental results illustrated the present sensor platform exhibited high sensitivity and selectivity in response to baicalein with a detection limit of 85 nmol·L^-1. The quenching mechanism is proved to be the inner filter effect. In addition, this sensor can also detect baicalein in biofluids (serum and urine) with good accuracy and reproducibility.