A high-speed optical sampling technique based on optoelectronic oscillators is proposed. Optoelectronic oscillators generate sampling pulses with high repetition rates and low time jitter directly, as a result, the time-domain multiplexing of low repetition rate sampling pulses is avoided,the system complexity is reduced, and the system efficiency is improved. The generated pulses are used to sample signals by time-domain Fourier transform, the amplitude information of the signals at different moments are modulated to the detection light at different wavelengths,then the light with different central wavelengths is filtered by wavelength division multiplexer or tunable filters, thus high-speed real-time sampling and serial-parallel conversion are realized, and electronic analog-to-digital conversion quantization with low rate is well matched. The optical pulses with repetition rate of 10 GHz and time jitter of 195 fs are generated in the experiments. Three kinds of signals with different waveforms are sampled, the sampling waveform is obtained, and the optical sampling rate of 40 GSa/s is reached. The experimental results show the feasibility of the proposed optical sampling technique based on optoelectronic oscillators.