The invention relates to the field of quantum secret communication. The invention discloses a high-speed local oscillator continuous variable quantum key distribution system and method. The system comprises an Alice terminal and a Bob terminal, wherein the Alice end is connected with the Bob end through an optical fiber channel, the Alice end comprises a first continuous laser module, an optical beam splitter, a quantum key modulation module, an optical attenuator, an optical frequency shift module and an optical beam combiner; and the Bob end comprises a second continuous laser module, an optical coupler, a balance detection module, an analog-to-digital conversion module, a digital signal processing module and a post-processing module. According to the invention, low-noise coherent detection of quantum signal light and high saturation of classic reference light can be flexibly realized, the system is simple, the cost is low, the repetition frequency and the safety code rate of the CVQKD system are greatly improved, and the practical process of the high-speed CVQKD system is further promoted.