A real-time and high-speed all-optical quantization scheme by slicing supercontinuum spectrum is studied experimentally in time domain. The optical filters are used to slice the supercontinuum spectrum generated by different intensity optical sampling pulses, so as to realize the real-time quantization of the optical sampling pulses. Optical sampling pulses with the repetition rate of 10 GHz are coupled into a 400-m highly nonlinear fiber after power amplification to generate supercontinuum spectrum, which is sliced by three tunable optical filters at different wavelengths. Real-time all-optical quantization with sampling rate of 10 GSa/s and quantization accuracy of 2 bits is realized based on slicing supercontinuum spectrum, and the extinction ratio among the quantized outputs can reach up to more than 10 dB.